Phase I Trial Characterizing the Pharmacokinetic Profile of N-803, a Chimeric IL-15 Superagonist, in Healthy Volunteers.

The oncotherapeutic promise of IL-15, a potent immunostimulant, is limited by a short serum t 1/2 The fusion protein N-803 is a chimeric IL-15 superagonist that has a >20-fold longer in vivo t 1/2 versus IL-15. This phase 1 study characterized the pharmacokinetic (PK) profile and safety of N-803 after s.c. administration to healthy human volunteers. Volunteers received two doses of N-803, and after each dose, PK and safety were assessed for 9 d. The primary endpoint was the N-803 PK profile, the secondary endpoint was safety, and immune cell levels and immunogenicity were measures of interest. Serum N-803 concentrations peaked 4 h after administration and declined with a t 1/2 of ∼20 h. N-803 did not cause treatment-emergent serious adverse events (AEs) or grade ≥3 AEs. Injection site reactions, chills, and pyrexia were the most common AEs. Administration of N-803 was well tolerated and accompanied by proliferation of NK cells and CD8+ T cells and sustained increases in the number of NK cells. Our results suggest that N-803 administration can potentiate antitumor immunity.

Ex vivo blockade of PI3K gamma or delta signaling enhances the antitumor potency of adoptively transferred CD8+ T cells.

Adoptive T cell transfer therapy induces objective responses in patients with advanced malignancies. Despite these results, some individuals do not respond due to the generation of terminally differentiated T cells during the expansion protocol. As the gamma and delta catalytic subunits in the PI3K pathway are abundant in leukocytes and involved in cell activation, we posited that blocking both subunits ex vivo with the inhibitor IPI-145 would prevent their differentiation, thereby increasing antitumor activity in vivo. However, IPI-145 treatment generated a product with reduced antitumor activity. Instead, T cells inhibited of PI3Kγ (IPI-549) or PI3Kδ (CAL-101 or TGR-1202) alone were more potent in vivo. While T cells coinhibited of PI3Kγ and PI3Kδ were less differentiated, they were functionally impaired, indicated by reduced production of effector cytokines after antigenic re-encounter and decreased persistence in vivo. Human CAR T cells expanded with either a PI3Kγ or PI3Kδ inhibitor possessed a central memory phenotype compared to vehicle cohorts. We also found that PI3Kδ-inhibited CARs lysed human tumors in vitro more effectively than PI3Kγ-expanded or traditionally expanded CAR T cells. Our data imply that sole blockade of PI3Kγ or PI3Kδ generates T cells with remarkable antitumor properties, a discovery that has substantial clinical implications.

Thioredoxin-1 improves the immunometabolic phenotype of antitumor T cells.

Adoptive transfer of tumor epitope-reactive T cells has emerged as a promising strategy to control tumor growth. However, chronically-stimulated T cells expanded for adoptive cell transfer are susceptible to cell death in an oxidative tumor microenvironment. Because oxidation of cell-surface thiols also alters protein functionality, we hypothesized that increasing the levels of thioredoxin (Trx), an antioxidant molecule facilitating reduction of proteins through cysteine thiol-disulfide exchange, in T cells will promote their sustained antitumor function. Using pre-melanosome protein (Pmel)-Trx1 transgenic mouse-derived splenic T cells, flow cytometry, and gene expression analysis, we observed here that higher Trx expression inversely correlated with reactive oxygen species and susceptibility to T-cell receptor restimulation or oxidation-mediated cell death. These Trx1-overexpressing T cells exhibited a cluster of differentiation 62Lhi (CD62Lhi) central memory-like phenotype with reduced glucose uptake (2-NBDGlo) and decreased effector function (interferon γlo). Furthermore, culturing tumor-reactive T cells in the presence of recombinant Trx increased the dependence of T cells on mitochondrial metabolism and improved tumor control. We conclude that strategies for increasing the antioxidant capacity of antitumor T cells modulate their immunometabolic phenotype leading to improved immunotherapeutic control of established tumors.

ALT-803, an IL-15 superagonist, in combination with nivolumab in patients with metastatic non-small cell lung cancer: a non-randomised, open-label, phase 1b trial.

BACKGROUND: Immunotherapy with PD-1 or PD-L1 blockade fails to induce a response in about 80% of patients with unselected non-small cell lung cancer (NSCLC), and many of those who do initially respond then develop resistance to treatment. Agonists that target the shared interleukin-2 (IL-2) and IL-15Rßγ pathway have induced complete and durable responses in some cancers, but no studies have been done to assess the safety or efficacy of these agonists in combination with anti-PD-1 immunotherapy. We aimed to define the safety, tolerability, and activity of this drug combination in patients with NSCLC. METHODS: In this non-randomised, open-label, phase 1b trial, we enrolled patients (aged ≥18 years) with previously treated histologically or cytologically confirmed stage IIIB or IV NSCLC from three academic hospitals in the USA. Key eligibility criteria included measurable disease, eligibility to receive anti-PD-1 immunotherapy, and an Eastern Cooperative Oncology Group performance status of 0 or 1. Patients received the anti-PD-1 monoclonal antibody nivolumab intravenously at 3 mg/kg (then 240 mg when US Food and Drug Administration [FDA]-approved dosing changed) every 14 days (either as new treatment or continued treatment at the time of disease progression) and the IL-15 superagonist ALT-803 subcutaneously once per week on weeks 1-5 of four 6-week cycles for 6 months. ALT-803 was administered at one of four escalating dose concentrations: 6, 10, 15, or 20 µg/kg. The primary endpoint was to define safety and tolerability and to establish a recommended phase 2 dose of ALT-803 in combination with nivolumab. Analyses were per-protocol and included any patients who received at least one dose of study treatment. This trial is registered with ClinicalTrials.gov, number NCT02523469; phase 2 enrolment of patients is ongoing. FINDINGS: Between Jan 18, 2016, and June 28, 2017, 23 patients were enrolled and 21 were treated at four dose levels of ALT-803 in combination with nivolumab. Two patients did not receive treatment because of the development of inter-current illness during enrolment, one patient due to leucopenia and one patient due to pulmonary dysfunction. No dose-limiting toxicities were recorded and the maximum tolerated dose was not reached. The most common adverse events were injection-site reactions (in 19 [90%] of 21 patients) and flu-like symptoms (15 [71%]). The most common grade 3 adverse events, occurring in two patients each, were lymphocytopenia and fatigue. A grade 3 myocardial infarction occurred in one patient. No grade 4 or 5 adverse events were recorded. The recommended phase 2 dose of ALT-803 is 20 µg/kg given once per week subcutaneously in combination with 240 mg intravenous nivolumab every 2 weeks. INTERPRETATION: ALT-803 in combination with nivolumab can be safely administered in an outpatient setting. The promising clinical activity observed with the addition of ALT-803 to the regimen of patients with PD-1 monoclonal antibody relapsed and refractory disease shows evidence of anti-tumour activity for a new class of agents in NSCLC. FUNDING: Altor BioScience (a NantWorks company), National Institutes of Health, and Medical University of South Carolina Hollings Cancer Center.

The clinical implications of immunogenomics in colorectal cancer: A path for precision medicine.

Colorectal cancer (CRC) remains the third most common malignancy and the second-leading cause of cancer-related deaths in the United States. Large multi-omic databases, such as The Cancer Genome Atlas and the International Colorectal Cancer Subtyping Consortium, have identified distinct molecular subtypes related to anatomy. The identification of genomic alterations in CRC is now critical because of the recent success and US Food and Drug Administration approval of pembrolizumab and nivolumab for microsatellite-instable tumors. In parallel, landmark studies have established the prognostic significance of the CRC tumor-infiltrating lymphocyte and the clinical impact of the tumor immune microenvironment. As a result, there is a growing appreciation for immunogenomics, the interconnected relation between tumor genomics and the immune microenvironment. The clinical implications of CRC immunogenomics continue to expand, and it will likely serve as a guide for next-generation immunotherapy strategies for improving outcomes for this disease. Cancer 2018;124:1650-9. © 2018 American Cancer Society.

A Novel Fusion of ALT-803 (Interleukin (IL)-15 Superagonist) with an Antibody Demonstrates Antigen-specific Antitumor Responses.

IL-15 and its receptor α (IL-15Rα) are co-expressed on antigen-presenting cells, allowing transpresentation of IL-15 to immune cells bearing IL-2RßγC and stimulation of effector immune responses. We reported previously that the high-affinity interactions between an IL-15 superagonist (IL-15N72D) and the extracellular IL-15Rα sushi domain (IL-15RαSu) could be exploited to create a functional scaffold for the design of multivalent disease-targeted complexes. The IL-15N72D·IL-15RαSuFc complex, also known as ALT-803, is a multimeric complex constructed by fusing IL-15N72D·IL-15RαSu to the Fc domain of IgG1. ALT-803 is an IL-15 superagonist complex that has been developed as a potent antitumor immunotherapeutic agent and is in clinical trials. Here we describe the creation of a novel fusion molecule, 2B8T2M, using the ALT-803 scaffold fused to four single chains of the tumor-targeting monoclonal antibody rituximab. This molecule displays trispecific binding activity through its recognition of the CD20 molecule on tumor cells, stimulation via IL-2RßγC displayed on immune effector cells, and binding to Fcγ receptors on natural killer cells and macrophages. 2B8T2M activates natural killer cells to enhance antibody-dependent cellular cytotoxicity, mediates complement-dependent cytotoxicity, and induces apoptosis of B-lymphoma cells. Compared with rituximab, 2B8T2M exhibits significantly stronger antitumor activity in a xenograft SCID mouse model and depletes B cells in cynomolgus monkeys more efficiently. Thus, ALT-803 can be modified as a functional scaffold for creating multispecific, targeted IL-15-based immunotherapeutic agents and may serve as a novel platform to improve the antitumor activity and clinical efficacy of therapeutic antibodies.

Murine Th17 cells utilize IL-2 receptor gamma chain cytokines but are resistant to cytokine withdrawal-induced apoptosis.

Adoptive cellular therapy (ACT) with the Th17 subset of CD4+ T cells can cure established melanoma in preclinical models and holds promise for treating human cancer. However, little is known about the growth factors necessary for optimal engraftment and anti-tumor activity of Th17 cells. Due to the central role of IL-2 receptor gamma chain (IL2Rγ-chain) cytokines (IL-2, IL-7, and IL-15) in the activity and persistence of many T cell subsets after adoptive transfer, we hypothesized that these cytokines are important for Th17 cells. We found that Th17 cells proliferated in response to IL-2, IL-7, and IL-15 in vitro. However, in contrast to many other T cell subsets, including conventionally activated CD8+ T cells, we found that Th17 cells were resistant to apoptosis in the absence of IL2Rγ-chain cytokines. To determine whether Th17 cells utilize IL2Rγ-chain cytokines in vivo, we tracked Th17 cell engraftment after adoptive transfer with or without cytokine depletion. Depletion of IL-7 and/or IL-2 decreased initial engraftment, while depletion of IL-15 did not. Supplementation of IL-2 increased initial Th17 engraftment. To assess the clinical relevance of these findings, we treated melanoma-bearing mice with Th17 cell adoptive transfer and concurrent cytokine depletion or supplementation. We found that simultaneous depletion of IL-2 and IL-7 decreased therapeutic efficacy, depletion of IL-15 had no effect, and IL-2 supplementation increased therapeutic efficacy. Our results show that Th17 cells are responsive to IL2Rγ-chain cytokines, and provide insight into the application of these cytokines for Th17-based therapeutic strategies.

The inducible costimulator augments Tc17 cell responses to self and tumor tissue.

The inducible costimulator (ICOS) plays a key role in the development of Th17 cells, but its role in the development and antitumor activity of IL-17-producing CD8(+) T cells (Tc17) remains unknown. We found that ICOS costimulation was important for the functional maintenance, but not differentiation, of Tc17 cells in vitro. Blocking the ICOS pathway using an antagonist mAb or by using recipient mice genetically deficient in the ICOS ligand reduced the antitumor activity of adoptively transferred Tc17 cells. Conversely, activating Tc17 cells with an ICOS agonist in vitro enhanced their capacity to eradicate melanoma and induce autoimmune vitiligo when infused into mice. However, ICOS stimulation did not augment the antitumor activity of IL-2 expanded T cells. Additional investigation revealed that ICOS stimulation not only increased IL-2Rα, CXCR3, and IL-23R expression on Tc17 cells, but also dampened their expression of suppressive molecule CD39. Although Tc17 cells activated with an ICOS agonist cosecreted heightened IL-17A, IL-9, and IFN-γ, their therapeutic effectiveness was critically dependent on IFN-γ production. Depletion of IL-17A and IL-9 had little impact on antitumor Tc17 cells activated with an ICOS agonist. Collectively, our work reveals that the ICOS pathway potentiates the antitumor activity of adoptively transferred Tc17 cells. This work has major implications for the design of vaccine, Ab and cell-based therapies for autoimmunity, infectious disease, and cancer.

Exploiting IL-17-producing CD4+ and CD8+ T cells to improve cancer immunotherapy in the clinic.

Cancer immunotherapy is one the most effective approaches for treating patients with tumors, as it bolsters the generation and persistence of memory T cells. In preclinical work, it has been reported that adoptively transferred CD4+ and CD8+ lymphocytes that secrete IL-17A (i.e., Th17 and Tc17 cells) regress tumors to a greater extent than IFN-γ(+)Th1 or Tc1 cells in vivo. Herein, we review the mechanisms underlying how infused Th17 and Tc17 cells regress established malignancies in clinically relevant mouse models of cancer. We also discuss how unique signaling cues--such as co-stimulatory molecules (ICOS and 41BB), cytokines (IL-12 and IL-23) or pharmaceutical reagents (Akt inhibitors, etc.)--can be exploited to bolster the therapeutic potential of IL-17(+) lymphocytes with an emphasis on using this knowledge to improve next-generation clinical trials for patients with cancer.

Interleukin-12 enhances the function and anti-tumor activity in murine and human CD8(+) T cells.

Mouse CD8(+) T cells conditioned with interleukin (IL)-12 ex vivo mediate the potent regression of established melanoma when transferred into lymphodepleted mice. However, the quantitative and qualitative changes induced by IL-12 in the responding mouse CD8(+) T cells have not been well defined. Moreover, the mechanisms by which IL-12-conditioning impacts human CD8(+) T cells, and how such cells might be expanded prior to infusion into patients is not known. We found that ex vivo IL-12-conditioning of mouse CD8(+) T cells led to a tenfold-100-fold increase in persistence and anti-tumor efficacy upon adoptive transfer into lymphodepleted mice. The enhancing effect of IL-12 was associated with maintenance of functional avidity. Importantly, in the context of ongoing ACT clinical trials, human CD8(+) T cells genetically modified with a tyrosinase-specific T cell receptor (TCR) exhibited significantly enhanced functional activity when conditioned with IL-12 as indicated by heightened granzyme B expression and elevated peptide-specific CD107a degranulation. This effect was sustainable despite the 20 days of in vitro cellular expansion required to expand cells over 1,000-fold allowing adequate cell numbers for administration to cancer patients. Overall, these findings support the efficacy and feasibility of ex vivo IL-12-conditioning of TCR-modified human CD8(+) T cells for adoptive transfer and cancer therapy.

Soluble IL-15/IL-15Rα complexes in human serum.

In this issue of Blood, Bergamaschi and colleagues demonstrate that effectively all circulating IL-15 found in the serum of humans and mice is associated with the soluble IL-15Rα.(1)

Brief research report: impact of vaccination on antibody responses and mortality from severe COVID-19.

Introduction: While it is established that vaccination reduces risk of hospitalization, there is conflicting data on whether it improves outcome among hospitalized COVID-19 patients. This study evaluated clinical outcomes and antibody (Ab) responses to severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) infection/vaccines in patients with acute respiratory failure (ARF) and various comorbidities. Methods: In this single-center study, 152 adult patients were admitted to Ohio State University hospital with ARF (05/2020 - 11/2022) including 112 COVID-19-positive and 40 COVID-19-negative patients. Of the COVID-19 positive patients, 23 were vaccinated for SARS-CoV-2 (Vax), and 89 were not (NVax). Of the NVax COVID-19 patients, 46 were admitted before and 43 after SARS-CoV-2 vaccines were approved. SARS-CoV-2 Ab levels were measured/analyzed based on various demographic and clinical parameters of COVID-19 patients. Additionally, total IgG4 Ab concentrations were compared between the Vax and NVax patients. Results: While mortality rates were 36% (n=25) and 27% (n=15) for non-COVID-19 NVax and Vax patients, respectively, in COVID-19 patients mortality rates were 37% (NVax, n=89) and 70% (Vax, n=23). Among COVID-19 patients, mortality rate was significantly higher among Vax vs. NVax patients (p=0.002). The Charlson's Comorbidity Index score (CCI) was also significantly higher among Vax vs. NVax COVID-19 patients. However, the mortality risk remained significantly higher (p=0.02) when we compared COVID-19 Vax vs. NVax patients with similar CCI score, suggesting that additional factors may increase risk of mortality. Higher levels of SARS-CoV-2 Abs were noted among survivors, suggestive of their protective role. We observed a trend for increased total IgG4 Ab, which promotes immune tolerance, in the Vax vs. NVax patients in week 3. Conclusion: Although our cohort size is small, our results suggest that vaccination status of hospital-admitted COVID-19 patients may not be instructive in determining mortality risk. This may reflect that within the general population, those individuals at highest risk for COVID-19 mortality/immune failure are likely to be vaccinated. Importantly, the value of vaccination may be in preventing hospitalization as opposed to stratifying outcome among hospitalized patients, although our data do not address this possibility. Additional research to identify factors predictive of aberrant immunogenic responses to vaccination is warranted.

Corrigendum: Brief research report: impact of vaccination on antibody responses and mortality from severe COVID-19.

[This corrects the article DOI: 10.3389/fimmu.2024.1325243.].

Translational and oncologic significance of tertiary lymphoid structures in pancreatic adenocarcinoma.

Pancreatic adenocarcinoma (PDAC) is an aggressive tumor with poor survival and limited treatment options. PDAC resistance to immunotherapeutic strategies is multifactorial, but partially owed to an immunosuppressive tumor immune microenvironment (TiME). However, the PDAC TiME is heterogeneous and harbors favorable tumor-infiltrating lymphocyte (TIL) populations. Tertiary lymphoid structures (TLS) are organized aggregates of immune cells that develop within non-lymphoid tissue under chronic inflammation in multiple contexts, including cancers. Our current understanding of their role within the PDAC TiME remains limited; TLS are complex structures with multiple anatomic features such as location, density, and maturity that may impact clinical outcomes such as survival and therapy response in PDAC. Similarly, our understanding of methods to manipulate TLS is an actively developing field of research. TLS may function as anti-tumoral immune niches that can be leveraged as a therapeutic strategy to potentiate both existing chemotherapeutic regimens and potentiate future immune-based therapeutic strategies to improve patient outcomes. This review seeks to cover anatomy, relevant features, immune effects, translational significance, and future directions of understanding TLS within the context of PDAC.

A workflow for targeted proteomics assay development using a versatile linear ion trap.

Advances in proteomics and mass spectrometry have enabled the study of limited cell populations, such as single-cell proteomics, where high-mass accuracy instruments are typically required. While triple quadrupoles offer fast and sensitive nominal resolution measurements, these instruments are effectively limited to targeted proteomics. Linear ion traps (LITs) offer a versatile, cost-effective alternative capable of both targeted and global proteomics. We demonstrate a workflow using a newly released, hybrid quadrupole-LIT instrument for developing targeted proteomics assays from global data-independent acquisition (DIA) measurements without needing high-mass accuracy. Gas-phase fraction-based DIA enables rapid target library generation in the same background chemical matrix as each quantitative injection. Using a new software tool embedded within EncyclopeDIA for scheduling parallel reaction monitoring assays, we show consistent quantification across three orders of magnitude of input material. Using this approach, we demonstrate measuring peptide quantitative linearity down to 25x dilution in a background of only a 1 ng proteome without requiring stable isotope labeled standards. At 1 ng total protein on column, we found clear consistency between immune cell populations measured using flow cytometry and immune markers measured using LIT-based proteomics. We believe hybrid quadrupole-LIT instruments represent an economic solution to democratizing mass spectrometry in a wide variety of laboratory settings.

Spatial and functional targeting of intratumoral Tregs reverses CD8+ T cell exhaustion and promotes cancer immunotherapy.

Intratumoral Tregs are key mediators of cancer immunotherapy resistance, including anti-programmed cell death (ligand) 1 [anti-PD-(L)1] immune checkpoint blockade (ICB). The mechanisms driving Treg infiltration into the tumor microenvironment (TME) and the consequence on CD8+ T cell exhaustion remain elusive. Here, we report that heat shock protein gp96 (also known as GRP94) was indispensable for Treg tumor infiltration, primarily through the roles of gp96 in chaperoning integrins. Among various gp96-dependent integrins, we found that only LFA-1 (αL integrin), and not αV, CD103 (αE), or ß7 integrin, was required for Treg tumor homing. Loss of Treg infiltration into the TME by genetic deletion of gp96/LFA-1 potently induced rejection of tumors in multiple ICB-resistant murine cancer models in a CD8+ T cell-dependent manner, without loss of self-tolerance. Moreover, gp96 deletion impeded Treg activation primarily by suppressing IL-2/STAT5 signaling, which also contributed to tumor regression. By competing for intratumoral IL-2, Tregs prevented the activation of CD8+ tumor-infiltrating lymphocytes, drove thymocyte selection-associated high mobility group box protein (TOX) induction, and induced bona fide CD8+ T cell exhaustion. By contrast, Treg ablation led to striking CD8+ T cell activation without TOX induction, demonstrating clear uncoupling of the 2 processes. Our study reveals that the gp96/LFA-1 axis plays a fundamental role in Treg biology and suggests that Treg-specific gp96/LFA-1 targeting represents a valuable strategy for cancer immunotherapy without inflicting autoinflammatory conditions.

mRNA vaccines against SARS-CoV-2 induce divergent antigen-specific T-cell responses in patients with lung cancer.

BACKGROUND: The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) Omicron variant is highly transmissible and evades pre-established immunity. Messenger RNA (mRNA) vaccination against ancestral strain spike protein can induce intact T-cell immunity against the Omicron variant, but efficacy of booster vaccination in patients with late-stage lung cancer on immune-modulating agents including anti-programmed cell death protein 1(PD-1)/programmed death-ligand 1 (PD-L1) has not yet been elucidated. METHODS: We assessed T-cell responses using a modified activation-induced marker assay, coupled with high-dimension flow cytometry analyses. Peripheral blood mononuclear cells (PBMCs) were stimulated with various viral peptides and antigen-specific T-cell responses were evaluated using flow cytometry. RESULTS: Booster vaccines induced CD8+ T-cell response against the ancestral SARS-CoV-2 strain and Omicron variant in both non-cancer subjects and patients with lung cancer, but only a marginal induction was detected for CD4+ T cells. Importantly, antigen-specific T cells from patients with lung cancer showed distinct subpopulation dynamics with varying degrees of differentiation compared with non-cancer subjects, with evidence of dysfunction. Notably, female-biased T-cell responses were observed. CONCLUSION: We conclude that patients with lung cancer on immunotherapy show a substantial qualitative deviation from non-cancer subjects in their T-cell response to mRNA vaccines, highlighting the need for heightened protective measures for patients with cancer to minimize the risk of breakthrough infection with the Omicron and other future variants.

Postinfusion PD-1+ CD8+ CAR T cells identify patients responsive to CD19 CAR T-cell therapy in non-Hodgkin lymphoma.

ABSTRACT: Chimeric antigen receptor (CAR) T-cell therapy has revolutionized treatment for relapsed/refractory B-cell non-Hodgkin lymphoma (NHL). Robust biomarkers and a complete understanding of CAR T-cell function in the postinfusion phase remain limited. Here, we used a 37-color spectral flow cytometry panel to perform high dimensional single-cell analysis of postinfusion samples in 26 patients treated with CD28 costimulatory domain containing commercial CAR T cells for NHL and focused on computationally gated CD8+ CAR T cells. We found that the presence of postinfusion Programmed cell death protein 1 (PD-1)+ CD8+ CAR T cells at the day 14 time point highly correlated with the ability to achieve complete response (CR) by 6 months. Further analysis identified multiple subtypes of CD8+ PD-1+ CAR T cells, including PD-1+ T cell factor 1 (TCF1)+ stem-like CAR T cells and PD-1+ T-cell immunoglobulin and mucin-domain containing-3 (TIM3)+ effector-like CAR T cells that correlated with improved clinical outcomes such as response and progression-free survival. Additionally, we identified a subset of PD-1+ CD8+ CAR+ T cells with effector-like function that was increased in patients who achieved a CR and was associated with grade 3 or higher immune effector cell-associated neurotoxicity syndrome. Here, we identified robust biomarkers of response to CD28 CAR T cells and highlight the importance of PD-1 positivity in CD8+ CAR T cells after infusion in achieving CR.

Antiviral CD4+ memory T cells are IL-15 dependent.

Survival and intermittent proliferation of memory CD4(+) and CD8(+) T cells appear to be controlled by different homeostatic mechanisms. In particular, contact with interleukin (IL)-15 has a decisive influence on memory CD8(+) cells, but not memory CD4(+) cells. Past studies of memory CD4(+) cells have relied heavily on the use of naturally occurring memory phenotype (MP) cells as a surrogate for antigen (Ag)-specific memory cells. However, we show here that MP CD4(+) cells contain a prominent subset of rapidly proliferating major histocompatibility complex (MHC) II-dependent cells. In contrast, Ag-specific memory CD4 cells have a slow turnover rate and are MHC II independent. In irradiated hosts, these latter cells ignore IL-15 and expand in response to the elevated levels of IL-7 in the lymphopenic hosts. In contrast, in normal nonlymphopenic hosts where IL-7 levels are low, memory CD4 cells are heavily dependent on IL-15. Significantly, memory CD4(+) responsiveness to endogenous IL-15 reflects marked competition from other cells, especially CD8(+) and natural killer cells, and increases considerably after removal of these cells. Therefore, under normal physiological conditions, homeostasis of CD8(+) and CD4(+) memory cells is quite similar and involves IL-15 and IL-7.