A Clinical Perspective on Plasma Cell Leukemia: A Single-Center Experience.

Circulating plasma cells (CPCs) are detected in most multiple myeloma (MM) patients, both at diagnosis and on relapse. A small subset, plasma cell leukemia (PCL), represents a different biology and has a poor prognosis. In this retrospective analysis, we evaluated patients with primary (pPCL, n = 35) or secondary (sPCL, n = 49), with ≥5% CPCs and a smaller subset with lower CPCs of 1-4% (n = 20). The median age was 61 years; 45% were men and 54% were Black. High-risk cytogenetics were found in 87% and extramedullary disease in 47%. For the entire cohort, 75% received a proteasome inhibitor, 70% chemotherapy, 54% an immunomodulatory drug, 24% a daratumumab-based regimen and 26% an autologous stem cell transplant (ASCT). The treatments marginally improved the overall survival (OS) for pPCL vs. sPCL (13 vs. 3.5 months p = 0.002). However, the 5-year survival for the whole cohort was dismal at 11%. High-risk cytogenetics, low platelets, extramedullary disease and high LDH were independently associated with poor outcomes. Further research is urgently needed to expand the treatment options and improve the outcomes in PCL.

Preventing trogocytosis by cathepsin B inhibition augments CAR T cell function.

Chimeric antigen receptor (CAR) T cell therapy has shown remarkable efficacy in cancer treatment. Still, most patients receiving CAR T cells relapse within 5 years of treatment. CAR-mediated trogocytosis (CMT) is a potential tumor escape mechanism in which cell surface proteins transfer from tumor cells to CAR T cells. CMT results in the emergence of antigen-negative tumor cells, which can evade future CAR detection, and antigen-positive CAR T cells, which is hypothesized to lead to CAR T cell fratricide and dysfunction. Using a system to selectively degrade trogocytosed antigen in CAR T cells, we show that the presence of trogocytosed antigen in CAR T cells directly causes CAR T cell fratricide and exhaustion. By performing a small molecule screening using a custom high throughput CMT-screening assay, we identified the cysteine protease cathepsin B (CTSB) as a key driver of CMT. We show that overexpression of cystatin A (CSTA), an endogenous human inhibitor of CTSB, reduces trogocytosis resulting in prolonged antitumor activity and increased CAR T cell expansion/persistence. Overall, we show that targeting CMT is an effective approach to enhance CAR T cell function, which may improve their clinical efficacy.

Treatment of secondary CNS lymphoma using CD19-targeted chimeric antigen receptor (CAR) T cells.

BACKGROUND: Aggressive B cell lymphoma with secondary central nervous system (CNS) involvement (SCNSL) carries a dismal prognosis. Chimeric antigen receptor (CAR) T cells (CAR-T) targeting CD19 have revolutionized the treatment for B cell lymphomas; however, only single cases with CNS manifestations successfully treated with CD19 CAR-T have been reported. METHODS: We prospectively enrolled 4 patients with SCNSL into our study to assess clinical responses and monitor T cell immunity. RESULTS: Two of four SNCSL patients responded to the CD19-targeted CAR-T. Only one patient showed a substantial expansion of peripheral (PB) CAR-T cells with an almost 100-fold increase within the first week after CAR-T. The same patient also showed marked neurotoxicity and progression of the SNCSL despite continuous surface expression of CD19 on the lymphoma cells and an accumulation of CD4+ central memory-type CAR-T cells in the CNS. Our studies indicate that the local production of chemokine IP-10, possibly through its receptor CXCR3 expressed on our patient's CAR-T, could potentially have mediated the local accumulation of functionally suboptimal anti-tumor T cells. CONCLUSIONS: Our results demonstrate expansion and homing of CAR-T cells into the CNS in SNCSL patients. Local production of chemokines such as IP-10 may support CNS infiltration by CAR-T cells but also carry the potential of amplifying local toxicity. Future studies investigating numbers, phenotype, and function of CAR-T in the different body compartments of SNSCL patients receiving CAR-T will help to improve local delivery of "fit" and highly tumor-reactive CAR-T with low off-target reactivity into the CNS.

Restricting CAR T Cell Trafficking Expands Targetable Antigen Space.

Chimeric antigen receptor (CAR) T cells are an effective treatment for some blood cancers. However, the lack of tumor-specific surface antigens limits their wider use. We identified a set of surface antigens that are limited in their expression to cancer and the central nervous system (CNS). We developed CAR T cells against one of these antigens, LINGO1, which is widely expressed in Ewing sarcoma (ES). To prevent CNS targeting, we engineered LINGO1 CAR T cells lacking integrin α4 (A4ko), an adhesion molecule essential for migration across the blood-brain barrier. A4ko LINGO1 CAR T cells were efficiently excluded from the CNS but retained efficacy against ES. We show that altering adhesion behavior expands the set of surface antigens targetable by CAR T cells.

A novel multicolor fluorescent spot assay for the functional assessment of chimeric antigen receptor (CAR) T-cell products.

BACKGROUND AIMS: Chimeric antigen receptor (CAR) T-cell (CAR-T) therapies have revolutionized the treatment of B-cell lymphomas. Unfortunately, relapses after CD19-targeted CAR-T are relatively common and, therefore, there is a critical need for assays able to assess the function and potency of CAR-T products pre-infusion, which will hopefully help to optimize CAR-T therapies. We developed a novel multicolor fluorescent spot assay (MFSA) for the functional assessment of CAR-T products on a single-cell level, combining the numerical assessment of CAR-T products with their functional characterization. METHODS: We first used a standard single-cell interferon (IFN)-γ enzyme-linked immune absorbent spot assay to measure CD19-targeted CAR-T responses to CD19-coated beads. We then developed, optimized and validated an MFSA that simultaneously measures the secretion of combinations of different cytokines on a single CAR-T level. RESULTS: We identified IFN-γ/tumor necrosis factor-α/granzyme B as the most relevant cytokine combination, and we used our novel MFSA to functionally and numerically characterize two clinical-grade CAR-T products. CONCLUSIONS: In conclusion, we have developed a novel assay for the quantitative and functional potency assessment of CAR-T products. Our optimized MFSA is cost-effective, easy to perform, reliable, can be performed overnight, allowing for a fast delivery of the product to the patient, and requires relatively minimal maintenance and training. The clinical value of our novel assay will be assessed in studies correlating the pre-infusion assessment of CAR-T products with the patients' outcome in a prospective fashion.

Immunomodulatory properties of CD38 antibodies and their effect on anticancer efficacy in multiple myeloma.

BACKGROUND: CD38 has been established as an important therapeutic target for multiple myeloma (MM), for which two CD38 antibodies are currently approved-daratumumab and isatuximab. CD38 is an ectoenzyme that degrades NAD and its precursors and is involved in the production of adenosine and other metabolites. AIM: Among the various mechanisms by which CD38 antibodies can induce MM cell death is immunomodulation, including multiple pathways for CD38-mediated T-cell activation. Patients who respond to anti-CD38 targeting treatment experience more marked changes in T-cell expansion, activity, and clonality than nonresponders. IMPLICATIONS: Resistance mechanisms that undermine the immunomodulatory effects of CD38-targeting therapies can be tumor intrinsic, such as the downregulation of CD38 surface expression and expression of complement inhibitor proteins, and immune microenvironment-related, such as changes to the natural killer (NK) cell numbers and function in the bone marrow niche. There are numerous strategies to overcome this resistance, which include identifying and targeting other therapeutic targets involved in, for example, adenosine production, the activation of NK cells or monocytes through immunomodulatory drugs and their combination with elotuzumab, or with bispecific T-cell engagers.

Systematic single amino acid affinity tuning of CD229 CAR T cells retains efficacy against multiple myeloma and eliminates on-target off-tumor toxicity.

T cells expressing chimeric antigen receptors (CARs) have shown remarkable therapeutic activity against different types of cancer. However, the wider use of CAR T cells has been hindered by the potential for life-threatening toxicities due to on-target off-tumor killing of cells expressing low amounts of the target antigen. CD229, a signaling lymphocyte-activation molecule (SLAM) family member, has previously been identified as a target for CAR T cell-mediated treatment of multiple myeloma (MM) due to its high expression on the surfaces of MM cells. CD229 CAR T cells have shown effective clearance of MM cells in vitro and in vivo. However, healthy lymphocytes also express CD229, albeit at lower amounts than MM cells, causing their unintended targeting by CD229 CAR T cells. To increase the selectivity of CD229 CAR T cells for MM cells, we used a single amino acid substitution approach of the CAR binding domain to reduce CAR affinity. To identify CARs with increased selectivity, we screened variant binding domains using solid-phase binding assays and biolayer interferometry and determined the cytotoxic activity of variant CAR T cells against MM cells and healthy lymphocytes. We identified a CD229 CAR binding domain with micromolar affinity that, when combined with overexpression of c-Jun, confers antitumor activity comparable to parental CD229 CAR T cells but lacks the parental cells' cytotoxic activity toward healthy lymphocytes in vitro and in vivo. The results represent a promising strategy to improve the efficacy and safety of CAR T cell therapy that requires clinical validation.

Imaging Biomarkers to Predict Outcomes in Patients With Large B-Cell Lymphoma With a Day 28 Partial Response by 18F-FDG PET/CT Imaging Following CAR-T Therapy.

BACKGROUND: CD19 directed CAR-T therapy for Large B-cell lymphoma (LBCL) has shown great therapeutic response in patients with relapsed/refractory disease with response rates of 60-80%. However, in patients with a partial response (PR) on initial day 28 post CAR-T therapy imaging, clinical uncertainty remains as half of these patients will ultimately have relapsed disease.   PATIENTS: In 24 patients receiving CD19 directed CAR-T therapy for relapsed/refractory LBCL achieving a PR on day 28, we utilize imaging biomarkers by 18F-FDG PET/CT imaging at pre CAR-T therapy baseline and day 28 to determine factors that may predict best overall response (B-OR), progression free survival (PFS), and overall survival (OS).   METHODS: Out of 75 patients receiving CAR-T therapy at a single institution, we retrospectively identified and reviewed 25 (33%) as achieving a PR on day 28. PR was defined using the 2014 Lugano classification system. All patients received standard of care CD19 directed CAR-T therapy with axicabtagene ciloleucel. Two independent nuclear medicine physicians measured baseline (pre-CAR-T therapy) and day 28 PET/CT SUVmax, SUVmean and TMV (cm3) of each lesion (node, organ or marrow uptake, if any) using ROVER software. All statistical tests were two-sided and conducted at the 0.05 level of significance. R version 1.3.1099 (R-studio) was used for statistical modeling.   CONCLUSION: We demonstrate that a higher day 28 SUVmax was significantly higher in those with a B-OR of PR and in our modeling, a lower day 28 SUVmax may predict favorable PFS and OS. Additionally, lower TMV, both at baseline and day 28, may also be predictive of longer PFS and OS, while lower TLG at baseline, but not day 28 is significantly associated with a B-OR of CR. While further study is warranted, these imaging biomarkers may allow for early identification of those with a day 28 PR at highest risk for relapse leading to early intervention to improve long term outcomes.

Chimeric antigen receptor (CAR) T cells for the treatment of a kidney transplant patient with post-transplant lymphoproliferative disorder (PTLD).

Post-transplant lymphoproliferative disorder (PTLD) is a potentially fatal complication following kidney transplantation, and there is a critical and unmet need for PTLD treatments associated with more pronounced and durable responses. To date, reports on the use of CD19-targeted chimeric antigen receptor (CAR) T (CAR-T) cells in patients after solid organ transplant (SOT) have been anecdotal, clinical presentations and outcomes have been heterogenous, and a longitudinal analysis of CAR-T cell expansion and persistence in PTLD patients has not been reported. Our report describes a patient with a history of renal transplant who received CD19-directed CAR-T cell therapy for the treatment of refractory PTLD, diffuse large B cell lymphoma (DLBCL)-type. We show that even with the background of prolonged immunosuppression for SOT, it is possible to generate autologous CAR-T products capable of expansion and persistence in vivo, without evidence of excess T-cell exhaustion. Our data indicate that CAR-T cells generated from a SOT recipient with PTLD can yield deep remissions without increased toxicity or renal allograft dysfunction. Future clinical studies should build on these findings to investigate CAR-T therapy, including longitudinal monitoring of CAR-T phenotype and function, for PTLD in SOT recipients.

Outcomes of Busulfan, Fludarabine, and 400 cGy Total Body Irradiation Compared With Busulfan and Fludarabine Reduced-Intensity Conditioning Regimens for Allogeneic Stem Cell Transplantation in Adult Patients With Hematologic Diseases: A Single-Center Experience.

BACKGROUND: Reduced intensity conditioning (RIC) regimens decrease the risk for nonrelapse mortality (NRM) in adult patients undergoing allogeneic hematopoietic stem cell transplantation for hematologic malignancies but increase the risk for relapse. The aim of this study was to compare the outcomes of fludarabine-total body irradiation (TBI) with fludarabine among patients with hematologic diseases. PATIENTS AND METHODS: This retrospective study of 137 patients with different hematologic malignancies compared the outcomes of 63 patients who received a conventional RIC regimen with 2 days of IV busulfan (3.2 mg/kg/d × 2 days) and fludarabine with 74 patients who received the same regimen plus 400 cGy of fludarabine and busulfan (FB)-TBI divided in 2 doses over 1 day (200 cGy BID). Median follow-up was 4.62 years. RESULTS: The donors were either HLA-matched siblings (36%) or HLA-matched unrelated donors (64%). The FB-TBI showed trends toward improvement in progression-free survival (PFS) and overall survival (OS) over FB (5-year PFS rates 50% vs 34%, P = .06, and 5-year OS rate 53% vs 39%, P = .13). Acute graft-vs-host disease (aGVHD), relapse, and NRM were similar between the 2 groups. The 5-year cumulative incidence of chronic GVHD (cGVHD) was lower in the FB-TBI group compared with the FB group (29% vs 52%, P = .003). Multivariable analysis revealed that grade III-IV aGVHD was the only independent risk factor for worse OS (P = .001) in both groups. A high disease risk index was possibly associated with inferior OS (P = .07) in both groups. CONCLUSIONS: The FB-TBI is a safe and effective intensified RIC regimen for adult patients with hematologic malignancies. It predicted a lower risk for cGVHD and showed possibly improved PFS and OS compared with FB.

Ocular adverse events associated with chimeric antigen receptor T-cell therapy: a case series and review.

BACKGROUND/AIMS: Chimeric antigen receptor T-cell (CAR T) therapy has been shown to improve the remission rate and survival for patients with refractory haematological malignancies. The aim of this study is to describe ocular adverse effects associated with CAR T therapy in patients with haematological malignancies. METHODS: This is a retrospective, single-institution, case series. Patients aged 18 years or older who received standard of care CAR T therapy for relapsed/refractory large B-cell lymphoma with a documented ophthalmic evaluation were included. The primary outcome was clinician ophthalmic examination findings. RESULTS: A total of 66 patients received CAR T-cell therapy from February 2018 to October 2019 with 11 receiving an ophthalmic examination. Eleven patients (n=22 eyes) who received CAR T-cell therapy were included in review. The median time from CAR T-cell infusion date to ocular examination was 57.5 days. The median patient age at the time of examination was 60.5 years. Ten patients had subjective symptoms prompting ophthalmic examination. Two patients reported floaters and photopsias. One patient had worsening ocular graft-versus-host disease. Two patients were identified with possible reactivation of viral infections, including herpes zoster ophthalmicus and regressing acute retinal necrosis. CONCLUSIONS: The increasing use of CAR T therapy for malignancies underscores the importance of ophthalmologists and oncologists understanding the potential toxicities associated with its use, particularly ocular toxicities and when to refer for an ophthalmic examination.

T cell responses against SARS-CoV-2 and its Omicron variant in a patient with B cell lymphoma after multiple doses of a COVID-19 mRNA vaccine.

Anti-SARS-CoV-2 antibodies are crucial for protection from future COVID-19 infections, limiting disease severity, and control of viral transmission. While patients with the most common type of hematologic malignancy, B cell lymphoma, often develop insufficient antibody responses to messenger RNA (mRNA) vaccines, vaccine-induced T cells would have the potential to 'rescue' protective immunity in patients with B cell lymphoma. Here we report the case of a patient with B cell lymphoma with profound B cell depletion after initial chemoimmunotherapy who received a total of six doses of a COVID-19 mRNA vaccine. The patient developed vaccine-induced anti-SARS-CoV-2 antibodies only after the fifth and sixth doses of the vaccine once his B cells had started to recover. Remarkably, even in the context of severe treatment-induced suppression of the humoral immune system, the patient was able to mount virus-specific CD4+ and CD8+ responses that were much stronger than what would be expected in healthy subjects after two to three doses of a COVID-19 mRNA vaccine and which were even able to target the Omicron 'immune escape' variant of the SARS-CoV-2 virus. These findings not only have important implications for anti-COVID-19 vaccination strategies but also for future antitumor vaccines in patients with cancer with profound treatment-induced immunosuppression.

Humoral immunity against SARS-CoV-2 variants including omicron in solid organ transplant recipients after three doses of a COVID-19 mRNA vaccine.

Objectives: Solid organ transplant recipients (SOTR) receiving post-transplant immunosuppression show increased COVID-19-related mortality. It is unclear whether an additional dose of COVID-19 vaccines can overcome the reduced immune responsiveness against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants. Methods: We analysed humoral immune responses against SARS-CoV-2 and its variants in 53 SOTR receiving SARS-CoV-2 vaccination. Results: Following the initial vaccination series, 60.3% of SOTR showed no measurable neutralisation and only 18.9% demonstrated neutralising activity of > 90%. More intensive immunosuppression, antimetabolites in particular, negatively impacted antiviral immunity. While absolute IgG levels were lower in SOTR than controls, antibody titres against microbial recall antigens were higher. By contrast, SOTR showed reduced vaccine-induced IgG/IgA antibody titres against SARS-CoV-2 and its delta variants and fewer linear B-cell epitopes, indicating reduced B-cell diversity. Importantly, a third vaccine dose led to an increase in anti-SARS-CoV-2 antibody titres and neutralising activity across alpha, beta and delta variants and to the induction of anti-SARS-CoV-2 CD4+ T cells in a subgroup of patients analysed. By contrast, we observed significantly lower antibody titres after the third dose with the omicron variant compared to the ancestral SARS-CoV-2 and the improvement in neutralising activity was much less pronounced than for all the other variants. Conclusion: Only a small subgroup of solid organ transplant recipients is able to generate functional antibodies after an initial vaccine series; however, an additional vaccine dose resulted in dramatically improved antibody responses against all SARS-CoV-2 variants except omicron where antibody responses and neutralising activity remained suboptimal.

Roadmap to affinity-tuned antibodies for enhanced chimeric antigen receptor T cell function and selectivity.

Chimeric antigen receptor (CAR) T cells have revolutionized cancer treatment. CARs use antibody-derived binding domains to redirect T cells to antigens expressed on the surface of cancer cells. However, the high affinity of most currently used CAR-binding domains results in excessive T-cell activation limiting CAR T-cell persistence and the inability to differentiate between antigen-high tumor cells and antigen-low healthy cells. We review recent data on the use of low-affinity CAR-binding domains and evaluate technologies and approaches to engineer and screen low-affinity antibody variants for CAR T-cell development. We propose an ideal workflow for the generation of optimal low-affinity binders derived from existing antibodies to streamline the development of more functional and selective therapeutics.