Minimal Residual Disease Status in Multiple Myeloma 1 Year After Autologous Hematopoietic Cell Transplantation and Lenalidomide Maintenance Are Associated With Long-Term Overall Survival.

PURPOSE: Prognostic Immunophenotyping in Myeloma Response (PRIMeR) is an ancillary study of minimal residual disease (MRD) assessment for multiple myeloma by next-generation multiparameter flow cytometry (MFC). Patients were enrolled on a three-arm randomized control trial (Blood and Marrow Transplants Clinical Trials Network 0702 Stem Cell Transplant for Myeloma in Combination of Novel Agents [STaMINA]; ClinicalTrials.gov identifier: NCT01109004). METHODS: Four hundred and thirty-five patients consented to the MRD panel, which included 10 monoclonal antibodies measured via six-color MFC. MRD was measured at baseline/preautologous hematopoietic cell transplant (BL/preAutoHCT), premaintenance (PM), and 1 year (Y1) after AutoHCT with a sensitivity of 10-5 to 10-6. The primary objective was to assess MRD-negative (MRDneg) at 1 year after AutoHCT and progression-free survival and overall survival (PFS/OS). RESULTS: Similar to the STaMINA results, at a median follow-up of 70 months, there was no significant difference in PFS/OS by treatment arm in the PRIMeR patients. MRDneg at all three time points was associated with significantly improved PFS, and MRDneg at Y1 had significantly longer OS. Multivariate analysis of PFS, adjusting for disease risk and treatment arm, demonstrated hazard ratios (HRs) in MRD-positive patients compared with MRDneg patients at BL, PM, and Y1 of 1.55 (P = .0074), 1.83 (P = .0007), and 3.61 (P < .0001), respectively. Corresponding HRs for OS were 1.19 (P = .48), 0.88 (P = .68), and 3.36 (P < .001). Patients with sustained MRDneg or who converted to MRDneg by Y1 had similar PFS/OS. CONCLUSION: To our knowledge, this first, prospective US cooperative group, multicenter study demonstrates that MRDneg at Y1 after AutoHCT with lenalidomide maintenance is prognostic for improved 6-year PFS and OS. Serial MRD measurements may direct trials to test how further therapy may improve long-term PFS and OS.

Probing cell proliferation: Considerations for dye selection.

Broadly speaking, cell tracking dyes are fluorescent compounds that bind stably to components on or within the cells so the fate of the labeled cells can be followed. Their staining should be bright and homogeneous without affecting cell function. For purposes of monitoring cell proliferation, each time a cell divides the intensity of cell tracking dye should diminish equally between daughter cells. These dyes can be grouped into two different classes. Protein reactive dyes label cells by reacting covalently but non-selectively with intracellular proteins. Carboxyfluorescein diacetate succinimidyl ester (CFSE) is the prototypic general protein label. Membrane intercalating dyes label cells by partitioning non-selectively and non-covalently within the plasma membrane. The PKH membrane dyes are examples of lipophilic compounds whose chemistry allows for their retention within biological membranes without affecting cellular growth, viability, or proliferation when used properly. Here we provide considerations based for labeling cell lines and peripheral blood mononuclear cells using both classes of dyes. Examples from optimization experiments are presented along with critical aspects of the staining procedures to help mitigate common risks. Of note, we present data where a logarithmically growing cell line is labeled with both a protein dye and a membrane tracking dye to compare dye loss rates over 6days. We found that dual stained cells paralleled dye loss of the corresponding single stained cells. The decrease in fluorescence intensity by protein reactive dyes, however, was more rapid than that with the membrane reactive dyes, indicating the presence of additional division-independent dye loss.

T Cell Exhaustion Markers in Multiple Myeloma Patients are Lower After Physical Activity Intervention.

PURPOSE: There is compelling evidence that CD4+ and CD8+T cells are dysfunctional in multiple myeloma, compromising their ability to control disease progression. Pre-clinical models suggest that exercise represents a non-pharmacologic means to reduce immune exhaustion, but no studies to date have examined the relationship between an exercise intervention and biomarkers of immune exhaustion in multiple myeloma patients. PATIENTS AND METHODS: The current study includes 24 multiple myeloma patients who participated in a six-month physical activity intervention, consisting of supervised strength training (n = 12) and unsupervised home-based walking arms (n = 12). Comprehensive flow cytometry was utilized to assess the frequency of CD4+ and CD8+T cells and subpopulations expressing the markers of exhaustion PD-1, TIGIT, TIM3 and/or LAG3. Ratios of exhausted to non-exhausted cell populations, and percentages of exhausted to total populations of the same lineage, were calculated for the baseline and final timepoints. RESULTS: Eighteen of 20 exhaustion measures were lower at the end of the intervention than at baseline, and several were significantly or borderline significantly reduced in the entire sample or in one of the arms. The entire sample saw improvements in the ratios of CD4+ TIGIT+ to non-exhausted CD4+ (0.7 [0.6] to 0.6 [0.4], P = .04) and CD8+ PD1+ to non-exhausted CD8+ (1.8 [2.6] to 1.5 [2.0], P = .06), and in total exhausted CD8+ as a percent of total CD8+ (72.9 [21.9] to 68.3 [19.6], P < .01). CONCLUSIONS: This pilot study suggests that physical activity induces changes in MM patients' immune systems, potentially rendering a less exhausted T cell state.

Outcomes of human leukocyte antigen-matched related donor and haploidentical allogeneic hematopoietic cell transplantation recipients by immune profiles of recipients and donors.

BACKGROUND: Haploidentical (Haplo) allogeneic HCTs (alloHCT) have been used more frequently over the last decade as survival is similar to HLA-matched related donor (MRD) alloHCTs. OBJECTIVE: We aimed to identify donor and recipient immune signatures before alloHCT that are associated with clinically meaningful outcomes in MRD vs Haplo alloHCT recipients. STUDY DESIGN: This retrospective cohort study of 165 MRD (n=132) and Haplo (n=33) alloHCT recipients and their related donors between 2007-2019 with paired peripheral blood samples immunophenotyped for T-cell, B-cell, NK cell and dendritic cell (DC) subsets. Immune cells were quantified before alloHCT in donors and recipients; calculations of immune cell ratios were classified as high, intermediate, and low and analyzed with alloHCT outcomes. RESULTS: Haplo donors were younger than MRD donors (median: 35 vs 51 years), whereas Haplo recipients were older than MRD recipients (median: 68 vs 54 years), were more likely to have a Karnofsky Performance Score ≤70 (76% vs 57%), 3+ comorbidities (54% vs 47%), and were in complete remission prior to alloHCT (58% vs 42%). In MRD alloHCT, a lower ratio of CD4+ to CD8+ effector memory cells in the donor was associated with lower 4-yr overall survival (OS; 25% v 61%; p=0.009), lower 4-yr progression free survival (PFS; 25% v 58%; p=0.014) and higher incidence of 1-yr transplant-related mortality (TRM; 39% v 7%; p=0.009) in recipients. A higher ratio of CD8+ effector memory to total NK cells measured in MRD recipients was associated with a higher incidence of grade II-IV aGvHD (63% v 37%; p=0.004) but was not statistically significant for III-IV aGvHD (23% v 12%). In Haplo alloHCT, a lower ratio of total T-regulatory to CD4+ central memory cells in the donor was associated with lower 4-yr PFS (22% v 60%; p=0.0091). A higher ratio of CD4+ effector memory to CD8+ effector memory cells measured in Haplo recipients pre-alloHCT was associated with lower 4-yr OS (25% v 88%; p=0.0039). In both MRD and Haplo recipients, a higher ratio of CD4+ naïve to CD4+ central memory cells was associated with a higher incidence of grade II-IV aGvHD (64% v 38%; p=0.04). CONCLUSION: Evaluation of pre-alloHCT immune signatures of the donor and recipient may influence clinically meaningful patient outcomes in both MRD and Haplo transplants.

Monitoring Cell Proliferation by Dye Dilution: Considerations for Panel Design.

High dimensional studies that include proliferation dyes face two inherent challenges in panel design. First, the more rounds of cell division to be monitored based on dye dilution, the greater the starting intensity of the labeled parent cells must be in order to distinguish highly divided daughter cells from background autofluorescence. Second, the greater their starting intensity, the more difficult it becomes to avoid spillover of proliferation dye signal into adjacent spectral channels, with resulting limitations on the use of other fluorochromes and ability to resolve dim signals of interest. In the third and fourth editions of this series, we described the similarities and differences between protein-reactive and membrane-intercalating dyes used for general cell tracking, provided detailed protocols for optimized labeling with each dye type, and summarized characteristics to be tested by the supplier and/or user when validating either dye type for use as a proliferation dye. In this fifth edition, we review: (a) Fundamental assumptions and critical controls for dye dilution proliferation assays; (b) Methods to evaluate the effect of labeling on cell growth rate and test the fidelity with which dye dilution reports cell division; and. (c) Factors that determine how many daughter generations can be accurately included in proliferation modeling. We also provide an expanded section on spectral characterization, using data collected for three protein-reactive dyes (CellTrace™ Violet, CellTrace™ CFSE, and CellTrace™ Far Red) and three membrane-intercalating dyes (PKH67, PKH26, and CellVue® Claret) on three different cytometers to illustrate typical decisions and trade-offs required during multicolor panel design. Lastly, we include methods and controls for assessing regulatory T cell potency, a functional assay that incorporates the "know your dye" and "know your cytometer" principles described herein.

Ofatumumab plus HyperCVAD/HD-MA induction leads to high rates of minimal residual disease negativity in patients with newly diagnosed mantle cell lymphoma: Results of a phase 2 study.

BACKGROUND: Ofatumumab is a humanized type 1 anti-CD20 monoclonal antibody. Preclinical studies show improved complement-mediated cytotoxicity (CMC) compared to rituximab in mantle cell lymphoma (MCL). This study evaluates the safety and efficacy of combining ofatumumab with HyperCVAD/MA (O-HyperCVAD) in newly diagnosed MCL. METHODS: In this single-arm phase 2 study, 37 patients were treated with the combination of O-HyperCVAD for 4 or 6 cycles, followed by high dose chemotherapy and autologous stem cell transplant. Primary objectives were overall response rate (ORR) and complete response (CR) rate at the end of therapy. Secondary objectives included minimal residual disease (MRD) negativity, progression-free survival (PFS), and overall survival (OS). RESULTS: Median age was 60 years; ORR was 86% and 73% achieved a CR by modified Cheson criteria. The MRD negativity rate was 78% after 2 cycles of therapy, increasing to 96% at the end of induction; median PFS and OS were 45.5 months and 56 months, respectively. Achieving a post-induction CR by both imaging and flow cytometry was associated with improved PFS and OS. Early MRD negativity (post-2 cycles) was also associated with an improved PFS but not OS. There were 3 deaths while on therapy, and grades 3 and 4 adverse events (AEs) were observed in 22% and 68% of the patients. CONCLUSION: The addition of ofatumumab to HyperCVAD/HD-MA led to high rates of MRD negativity by flow cytometry in patients with newly diagnosed MCL. Achieving a CR post-induction by both imaging and flow cytometry is associated with improved overall survival.

Circulating CD14+ HLA-DRlo/- monocytic cells as a biomarker for epithelial ovarian cancer progression.

PROBLEM: Previous studies identified circulating CD14+ HLA-DRlo/- monocytic cells as an immune suppressive subset in solid malignancies, such as prostate, renal cell carcinoma, and pancreatic cancer. Such monocytic cells have been implicated not only in tumour progression but also as a potential barrier for immunotherapy. This study examined the relationship between the frequency of circulating monocytic cells and epithelial ovarian cancer (EOC) progression pre- and post-frontline chemotherapy, defined by disease stage, which is a leading prognostic factor for this malignancy. METHOD OF STUDY: Incident cases of 236 women with EOC were recruited and comprehensive flow cytometry was utilized to assess the frequency of peripheral blood CD33+ CD11b+ HLA-DR-/low CD14+ CD15- monocytic cells, henceforth termed CD14+ HLA-DRlo/- monocytic cells, prior to and after completion of frontline chemotherapy. Multivariable odds ratios (OR) were used to estimate the association between CD14+ HLA-DRlo/- monocytic cell percentages and disease stage. Wilcoxon signed-rank tests evaluated changes in these monocytic cell levels pre- and post-chemotherapy in a patient subset (n = 70). RESULTS: Patients with elevated frequencies of circulating CD14+ HLA-DRlo/- monocytic cells at diagnosis were at 3.33-fold greater odds of having advanced stage (III/IV) EOC (CI: 1.04-10.64), with a significant trend in increasing CD14+ HLA-DRlo/- monocytic cell levels (P = .04). There was a 2.02% median decrease of these monocytic cells post-chemotherapy among a subset of patients with advanced stage disease (P < .0001). CONCLUSION: These findings support the potential clinical relevance of CD14+ HLA-DRlo/- monocytic cells in EOC for prognosis and may indicate a non-invasive biomarker to measure disease progression.

Phase I Clinical Trial of Combination Propranolol and Pembrolizumab in Locally Advanced and Metastatic Melanoma: Safety, Tolerability, and Preliminary Evidence of Antitumor Activity.

PURPOSE: Increased ß-adrenergic receptor (ß-AR) signaling has been shown to promote the creation of an immunosuppressive tumor microenvironment (TME). Preclinical studies have shown that abrogation of this signaling pathway, particularly ß2-AR, provides a more favorable TME that enhances the activity of anti-PD-1 checkpoint inhibitors. We hypothesize that blocking stress-related immunosuppressive pathways would improve tumor response to immune checkpoint inhibitors in patients. Here, we report the results of dose escalation of a nonselective ß-blocker (propranolol) with pembrolizumab in patients with metastatic melanoma. PATIENTS AND METHODS: A 3 + 3 dose escalation study for propranolol twice a day with pembrolizumab (200 mg every 3 weeks) was completed. The primary objective was to determine the recommended phase II dose (RP2D). Additional objectives included safety, antitumor activity, and biomarker analyses. Responders were defined as patients with complete or partial response per immune-modified RECIST at 6 months. RESULTS: Nine patients with metastatic melanoma received increasing doses of propranolol in cohorts of 10, 20, and 30 mg twice a day. No dose-limiting toxicities were observed. Most common treatment-related adverse events (TRAEs) were rash, fatigue, and vitiligo, observed in 44% patients. One patient developed two grade ≥3 TRAEs. Objective response rate was 78%. While no significant changes in treatment-associated biomarkers were observed, an increase in IFNγ and a decrease in IL6 was noted in responders. CONCLUSIONS: Combination of propranolol with pembrolizumab in treatment-naïve metastatic melanoma is safe and shows very promising activity. Propranolol 30 mg twice a day was selected as RP2D in addition to pembrolizumab based on safety, tolerability, and preliminary antitumor activity.

CD319 (SLAMF7) an alternative marker for detecting plasma cells in the presence of daratumumab or elotuzumab.

BACKGROUND: Daratumumab is an anti-CD38 immunotherapeutic drug that has increasingly been used to treat patients with heavily pre-treated and relapsed/refractory multiple myeloma. In so doing, the detection of CD38 antigen on plasma cells by flow cytometry is impeded. We hypothesized that alternative markers can be used in place or in addition to CD38 when detecting plasma cells post-treated with daratumumab. METHODS: A total of 16 alternative markers were tested using 22 bone marrow aspirates from patients with plasma cell neoplasm. The ability of selected markers to discern plasma cells from other hematopoietic cells were evaluated. The stability of tested markers when stored at 4 or 25°C after T = 0, 24, 48, and 72 h was also established. Finally, selected markers were incorporated into a panel used for monitoring multiple myeloma measurable residual disease to test their utility to identify plasma cells in the presence of daratumumab and/or elotuzumab (anti-CD319) drugs. RESULTS: Out of the 16 tested markers, CD319, CD54, CD229, CD317, and p63 were expressed by >90% of the plasma cells. Only CD319, CD54, and CD229 achieved 100% detection sensitivity. Further analysis showed that CD319 was better than CD229 and CD54 at resolving plasma cells from background hematopoietic cells, with CD54 being the worst (resolution metric, mean ± SD: CD319 [2.04 ± 0.86]; CD229 [1.47 ± 0.45]; and CD54 [1.22 ± 0.60]). CD229 was expressed by >90% of T lymphocytes, whereas CD319 was expressed preferentially by the CD8+ T cells and less frequently in CD4+ T cells. Additionally, CD229 was found on >60% of B and NK cells, as well as minor subsets of monocytes and granulocytes. CD319 was expressed on most NK cells and a minor subset of B cells, granulocytes, and monocytes. Even though CD229 and CD319 were expressed by different leukocyte subsets, their expression levels were highest on plasma cells. The expression of CD138 on plasma cells was significantly lower after storage at 4°C, while the expression levels of CD38, CD229, and CD319 remained stable at 4 or 25°C. Using limiting dilution experiments, the treatment of cells with daratumumab severely impeded the detection of CD38 antigen on plasma cells, whereas elotuzumab treatment did not block detection of CD319 on plasma cells. CONCLUSIONS: CD319 is a suitable alternative to CD38 for identifying plasma cells. Our results showed that a panel used for monitoring multiple myeloma measurable residual disease could be modified by using CD319 alone or in combination with CD38 to detect PCs in daratumumab or elotuzumab treated patients.

Low-Level Cytomegalovirus Antigenemia Promotes Protective Cytomegalovirus Antigen-Specific T Cells after Allogeneic Hematopoietic Cell Transplantation.

Previous studies have reported a beneficial effect from cytomegalovirus (CMV) reactivation after allogeneic hematopoietic stem cell transplantation (alloHCT) on immune reconstitution. We determined the CMV antigenemia level associated with increased CMV antigen-specific T cells (CASTs) at day +100 and decreased CMV reactivation after day +100. CMV reactivation and CASTs were measured with CMV antigenemia and CMV-specific major histocompatibility complex multimers. The analysis consisted of 775 CAST measurements obtained before and 30, 100, and 365 days post-alloHCT from 327 consecutive patients treated between 2008 and 2016. Detectable CASTs correlated with recipient (P < .0001) and donor (P < .0001) CMV seropositivity pre-alloHCT. CMV reactivation before day +100 was associated with a higher proportion of patients who achieved ≥3 CASTs/µL by day +100 (61% with versus 39% without reactivation, P < .001). In alloHCT recipients at high risk for CMV reactivation (R+D±) with a maximum of grade II acute graft-versus-host-disease, reactivating CMV before day +100 and achieving ≥3 versus <3 CASTs/µL at day +100 was associated with reduced CMV reactivation from day +100 to +365 (27% versus 62%, P = .04). This protective effect was observed with low-level but not high-level CMV reactivation (<5 versus ≥5/50,000 polymorphonuclear leukocytes + pp65, respectively). These findings suggest low-level CMV reactivation may be beneficial and that treatment may be delayed until progression. These findings will need validation in prospective clinical trials using CMV PCR and antigenemia assays.

Quantification of Early-Stage Myeloid-Derived Suppressor Cells in Cancer Requires Excluding Basophils.

Myeloid derived suppressor cells (MDSC) are a heterogeneous group of immature cells that accumulate in the peripheral blood and tumor microenvironment and are barriers to cancer therapy. MDSCs serve as prognostic biomarkers and are targets for therapy. On the basis of surface markers, three subsets of MDSCs have been defined in humans: granulocytic, monocytic, and early stage (e-MDSC). The markers attributed to e-MDSCs overlap with those of basophils, which are rare circulating myeloid cells with unrecognized roles in cancer. Thus, we asked whether e-MDSCs in circulation and the tumor microenvironment include basophils. On average, 58% of cells with e-MDSC surface markers in blood and 36% in ascites from patients with ovarian cancer were basophils based on CD123high expression and cytology, whereas cells with immature features were rare. Circulating and ascites basophils did not suppress proliferation of stimulated T cells, a key feature of MDSCs. Increased accumulation of basophils and basogranulin, a marker of basophil degranulation, were observed in ascites compared to serum in patients with newly diagnosed ovarian cancer. Basophils recruited to the tumor microenvironment may exacerbate fluid accumulation by their release of proinflammatory granular constituents that promote vascular leakage. No significant correlation was observed between peripheral basophil counts and survival in patients with ovarian cancer. Our results suggest that studies in which e-MDSCs were defined solely by surface markers should be reevaluated to exclude basophils. Both immaturity and suppression are criteria to define e-MDSCs in future studies.

Correction: Immune profiling in diffuse large B-cell lymphoma and mantle cell lymphoma patients treated with autologous hematopoietic cell transplant.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Immune profiling in diffuse large B-cell lymphoma and mantle cell lymphoma patients treated with autologous hematopoietic cell transplant.

This is the first longitudinal study of immune profiles and autologous hematopoietic cell transplant (AHCT) survival in B-cell non-Hodgkin lymphoma (B-NHL) patients and the effect of plerixafor mobilization on immune reconstitution in this population. A comprehensive immunophenotyping panel was performed in 104 consecutive adult B-NHL patients (58% diffuse large B cell and 42% mantle cell) who received AHCT (1/2008-11/2014), at a median of 28 days pre-AHCT (N = 104) and Day +100 (N = 83) post-AHCT. Median follow-up post-AHCT was 61 months (range: 8-120 months). Compared to patients mobilized with filgrastim and plerixafor, patients mobilized with filgrastim alone had a higher proportion of CD4+ naïve (p = 0.006) and CD8+ central memory T-cells (p = 0.006) pre-AHCT. For patients transplanted in complete remission (CR), a higher proportion of CD8+ effector memory T-cells pre-AHCT was associated with worse progression-free survival (PFS; p < 0.01) and overall survival (OS; p < 0.01). A higher ratio of CD8:CD4+ central memory T-cells pre-AHCT was associated with worse PFS (p < 0.0001) and OS (p = 0.0034). This same ratio measured post-AHCT among patients in CR on Day +100 was associated with worse and OS (p = 0.008) but not PFS (p = not significant). These immune subsets are complementary biomarkers which identify patients transplanted in CR who have poor survival prognoses and may warrant further clinical interventions.

Methodological considerations for the high sensitivity detection of multiple myeloma measurable residual disease.

BACKGROUND: Recent advances in therapeutic interventions have dramatically improved complete response rates in patients with multiple myeloma (MM). The ability to identify residual myeloma cells (e.g., measurable residual disease [MRD]) can provide valuable information pertaining to patient's depth of response to therapy and risk of relapse. Multiparametric flow cytometry is an excellent technique to monitor MRD and has been demonstrated to correlate with patient outcome post-treatment. To achieve the high sensitivity (one abnormal cell in 105 -106 cells) required for MRD evaluation, millions of cells have to be acquired and conventional immunophenotyping protocols are unable to attain these numbers, indicating the needs for alternative flow cytometric staining procedures. A bulk, "Pre-lysis" method is the consensus approach for staining large number of cells, requires two red blood cell lysis steps, and can adversely affect epitope density. In this study, we tested the "Pooled-tube" and "Dextran Sedimentation" staining procedures and correlated them with the "Pre-lysis" method as potential alternative approaches. METHODS: A total of 22 bone marrow aspirates from patients with plasma cell (PC) dyscrasia were processed in parallel using the "Pre-lysis," "Pooled-tube," and "Dextran Sedimentation" techniques. Stain indices were calculated and compared to assess their impacts on staining performance for each antibody used in the consensus panel. The recovery of normal and abnormal PCs, mast cells, and B cell precursors was enumerated and compared after their counts were normalized using fluorescent beads. The limit of blank, limit of detection, and lower limit of quantification were established using serial dilution experiments. RESULTS: The staining performances of CD19 PECy7, CD27 BV510, CD81 APCH7, and CD138 BV421 were improved using the "Pooled-tube" method when compared to "Pre-lysis." "Pre-lysis" was better at resolving CD56 using clone C5.9 but our results demonstrated similar improvement can also be achieved by "Pooled-tube" when alternative CD56 PE clones were used. "Dextran sedimentation" yielded similar staining results when compared to "Pre-lysis" for all the markers analyzed. The "Pooled-tube" method, when normalized to "Pre-lysis," recovered higher numbers of total PCs (1.2 ± 0.2 times higher; p = .049), normal PCs (1.4 ± 0.26; p = .007), mast cells (1.46 ± 0.27; p = .003), and B cell precursors (1.42 ± 0.3; p = .011), but not abnormal PCs (1.09 ± 0.2; p = .352). There was no evidence that the recovery of cells was different between "Pre-lysis" versus "Dextran Sedimentation." All three flow cytometric assays achieved a minimum sensitivity of 10-5 and approached that of 10-6 for detecting rare events. CONCLUSION: Both "Pooled-tube" and "Dextran Sedimentation" staining procedures were comparable to the "Pre-lysis" method and are suitable high sensitivity flow cytometric approaches that can be used to process bone marrow samples for MM MRD testing.

BMT CTN Myeloma Intergroup Workshop on Minimal Residual Disease and Immune Profiling: Summary and Recommendations from the Organizing Committee.

The Blood and Marrow Transplant Clinical Trials Network Myeloma Intergroup Workshop on Minimal Residual Disease and Immune Profiling was convened on December 1, 2016 at the American Society of Hematology meeting to discuss the emerging data and technologies for minimal residual disease assessment and immune profiling in myeloma. Particular emphasis was placed on developing strategies to incorporate these techniques into clinical trial design. This document reviews the literature, summarizes the topics discussed in the workshop, and provides recommendations for integration of these techniques into future clinical trial design.

Monitoring Cell Proliferation by Dye Dilution: Considerations for Probe Selection.

In the third edition of this series, we described protocols for labeling cell populations with tracking dyes, and addressed issues to be considered when combining two different tracking dyes with other phenotypic and viability probes for the assessment of cytotoxic effector activity and regulatory T cell functions. We summarized key characteristics of and differences between general protein and membrane labeling dyes, discussed determination of optimal staining concentrations, and provided detailed labeling protocols for both dye types. Examples of the advantages of two-color cell tracking were provided in the form of protocols for: (a) independent enumeration of viable effector and target cells in a direct cytotoxicity assay; and (b) an in vitro suppression assay for simultaneous proliferation monitoring of effector and regulatory T cells.The number of commercially available fluorescent cell tracking dyes has expanded significantly since the last edition, with new suppliers and/or new spectral properties being added at least annually. In this fourth edition, we describe evaluations to be performed by the supplier and/or user when characterizing a new cell tracking dye and by the user when selecting one for use in multicolor proliferation monitoring. These include methods for: (a) Assessment of the dye's spectral profile on the laboratory's flow cytometer(s) to optimize compatibility with other employed fluorochromes and minimize compensation problems; (b) Evaluating the effect of labeling on cell growth rate;

Diagnosis of Plasma Cell Dyscrasias and Monitoring of Minimal Residual Disease by Multiparametric Flow Cytometry.

Plasma cell dyscrasia (PCD) is a heterogeneous disease that has seen a tremendous change in outcomes due to improved therapies. Over the past few decades, multiparametric flow cytometry has played an important role in the detection and monitoring of PCDs. Flow cytometry is a high-sensitivity assay for early detection of minimal residual disease (MRD) that correlates well with progression-free survival and overall survival. Before flow cytometry can be effectively implemented in the clinical setting, sample preparation, panel configuration, analysis, and gating strategies must be optimized to ensure accurate results. Current consensus methods and reporting guidelines for MRD testing are discussed.

Immune signatures associated with improved progression-free and overall survival for myeloma patients treated with AHSCT.

Multiple therapeutic options exist for multiple myeloma (MM), including autologous hematopoietic stem cell transplantation (AHSCT). Measurement of minimal residual disease (MRD) and immune reconstitution is rapidly becoming an integral part of the care of MM patients. We investigated comprehensive immune profiling (IP) associated with progression-free survival (PFS) and overall survival (OS). From August 2007 to January 2014, 101 consecutive MM patients underwent peripheral blood IP and marrow MRD testing before and approximately 100 days after AHSCT. Higher pre-AHSCT CD19+ B-cell counts correlated with improved 2-year PFS (83% [highest quartile] vs 53% [lowest quartile]; P = .01) and OS (93% [highest quartile] vs 63% [lowest quartile]; P = .0003). This effect was seen primarily in patients with MRD-positive marrow tests. Higher γδ T-cell counts post-AHSCT correlated with improved 2-year PFS (65% [highest quartile] vs 45% [lowest quartile]; P = .02) and OS (89% [highest quartile] vs 65% [lowest quartile]; P = .01). Higher CD4+ central memory (CM) cell counts post-AHSCT were associated with improved 2-year OS (95% [upper quartile] vs 47% [lowest quartile]; P = .0003) but not PFS. The higher γδ T-cell and CD4+ CM-cell count associations were primarily observed in MRD-negative patients post-AHSCT and in patients not receiving maintenance therapy. This proof-of-concept study demonstrates that IP before and after AHSCT can be of complementary prognostic value for depth of response. Maintenance therapy seems to overcome negative IP. IP and MRD should be measured in clinical trials of maintenance therapy with novel agents post-AHSCT for MM to confirm their utility for prognosis and management.

Simultaneous, Single-Cell Measurement of Messenger RNA, Cell Surface Proteins, and Intracellular Proteins.

Nucleic acid content can be quantified by flow cytometry through the use of intercalating compounds; however, measuring the presence of specific sequences has hitherto been difficult to achieve by this methodology. The primary obstacle to detecting discrete nucleic acid sequences by flow cytometry is their low quantity and the presence of high background signals, rendering the detection of hybridized fluorescent probes challenging. Amplification of nucleic acid sequences by molecular techniques such as in situ PCR have been applied to single-cell suspensions, but these approaches have not been easily adapted to conventional flow cytometry. An alternative strategy implements a Branched DNA technique, comprising target-specific probes and sequentially hybridized amplification reagents, resulting in a theoretical 8,000- to 16,000-fold increase in fluorescence signal amplification. The Branched DNA technique allows for the quantification of native and unmanipulated mRNA content with increased signal detection and reduced background. This procedure utilizes gentle fixation steps with low hybridization temperatures, leaving the assayed cells intact to permit their concomitant immunophenotyping. This technology has the potential to advance scientific discovery by correlating potentially small quantities of mRNA with many biological measurements at the single-cell level.

Dextramer reagents are effective tools for quantifying CMV antigen-specific T cells from peripheral blood samples.

The enumeration of antigen-specific T cells is increasingly relevant in clinical and research settings. This information is useful for evaluating immune responses to treatment, monitoring the efficacy of anticancer vaccines, and for detecting self-reactive T cells in autoimmune disorders. Quantifying antigen-specific T cells can be accomplished via IFNγ ELISpot assay, the measurement of intracellular cytokine production by flow cytometry, or by lymphocyte proliferation assays in response to antigen. While robust, these technologies are labor-intensive and can take several days to obtain results. New technology has led to more powerful tools for quickly and accurately measuring antigen-specific T cells by flow cytometry via fluorescently-labeled TCR-specific multimers. In this study, we evaluated the use of an assay based on Dextramer reagents for enumerating cytomegalovirus (CMV) antigen-specific T cells (CASTs). Assay performance characteristics were assessed by establishing Dextramers' sensitivity (median=0.4; range=0.1-1.4 CASTs µl(-1) ), determining their specificity (100%), evaluating assay robustness with different leukocyte sources and assay reproducibility via interlaboratory and interinstrument investigations. Furthermore, the levels of CASTs in 95 peripheral blood samples from 62 unique blood and marrow transplants recipients correlated well between Dextramers and Tetramers (R(2) =0.9042).