Immunogenicity of CAR T cells in cancer therapy

Patient-derived T cells genetically reprogrammed to express CD19-specific chimeric antigen receptors (CARs) have shown remarkable clinical responses and are commercially available for the treatment of patients with certain advanced-stage B cell malignancies. Nonetheless, several trials have revealed pre-existing and/or treatment-induced immune responses to the mouse-derived single-chain variable fragments included in these constructs. These responses might have contributed to both treatment failure and the limited success of redosing strategies observed in some patients. Data from early phase clinical trials suggest that CAR T cells are also associated with immunogenicity-related events in patients with solid tumours. Generally, the clinical implications of anti-CAR immune responses are poorly understood and highly variable between different CAR constructs and malignancies. These observations highlight an urgent need to uncover the mechanisms of immunogenicity in patients receiving CAR T cells and develop validated assays to enable clinical detection. In this Review, we describe the current clinical evidence of anti-CAR immune responses and discuss how new CAR T cell technologies might impact the risk of immunogenicity. We then suggest ways to reduce the risks of anti-CAR immune responses to CAR T cell products that are advancing towards the clinic. Finally, we summarize measures that investigators could consider in order to systematically monitor and better comprehend the possible effects of immunogenicity during trials involving CAR T cells as well as in routine clinical practice.

Targeting the membrane-proximal C2-set domain of CD33 for improved CD33-directed immunotherapy

There is increasing interest in targeting CD33 in malignant and non-malignant disorders. In acute myeloid leukemia, longer survival with the CD33 antibody-drug conjugate gemtuzumab ozogamicin (GO) validates this strategy. Still, GO benefits only some patients, prompting efforts to develop more potent CD33-directed therapeutics. As one limitation, CD33 antibodies typically recognize the membrane-distal V-set domain. Using various artificial CD33 proteins, in which this domain was differentially positioned within the extracellular portion of the molecule, we tested whether targeting membrane-proximal targeting epitopes enhances the effector functions of CD33 antibody-based therapeutics. Consistent with this idea, a CD33^V-set/CD3 bispecific antibody (BsAb) and CD33^V-set-directed chimeric antigen receptor (CAR)-modified T cells elicited substantially greater cytotoxicity against cells expressing a CD33 variant lacking the entire C2-set domain than cells expressing full-length CD33, whereas cytotoxic effects induced by GO were independent of the position of the V-set domain. We therefore raised murine and human antibodies against the C2-set domain of human CD33 and identified antibodies that bound CD33 regardless of the presence/absence of the V-set domain (“CD33^PAN antibodies”). These antibodies internalized when bound to CD33 and, as CD33^PAN/CD3 BsAb, had potent cytolytic effects against CD33⁺ cells. Together, our data provide rationale for further development of CD33^PAN antibody-based therapeutics.

Factors associated with outcomes after a second CD19-targeted CAR T-cell infusion for refractory B-cell malignancies

CD19-targeted chimeric antigen receptor-engineered (CD19 CAR) T-cell therapy has shown significant efficacy for relapsed or refractory (R/R) B-cell malignancies. Yet, CD19 CAR T cells fail to induce durable responses in most patients. Second infusions of CD19 CAR T cells (CART2) have been considered as a possible approach to improve outcomes. We analyzed data from 44 patients with R/R B-cell malignancies (acute lymphoblastic leukemia [ALL], n = 14; chronic lymphocytic leukemia [CLL], n = 9; non-Hodgkin lymphoma [NHL], n = 21) who received CART2 on a phase 1/2 trial (NCT01865617) at our institution. Despite a CART2 dose increase in 82% of patients, we observed a low incidence of severe toxicity after CART2 (grade ≥3 cytokine release syndrome, 9%; grade ≥3 neurotoxicity, 11%). After CART2, complete response (CR) was achieved in 22% of CLL, 19% of NHL, and 21% of ALL patients. The median durations of response after CART2 in CLL, NHL, and ALL patients were 33, 6, and 4 months, respectively. Addition of fludarabine to cyclophosphamide-based lymphodepletion before the first CAR T-cell infusion (CART1) and an increase in the CART2 dose compared with CART1 were independently associated with higher overall response rates and longer progression-free survival after CART2. We observed durable CAR T-cell persistence after CART2 in patients who received cyclophosphamide and fludarabine (Cy-Flu) lymphodepletion before CART1 and a higher CART2 compared with CART1 cell dose. The identification of 2 modifiable pretreatment factors independently associated with better outcomes after CART2 suggests strategies to improve in vivo CAR T-cell kinetics and responses after repeat CAR T-cell infusions, and has implications for the design of trials of novel CAR T-cell products after failure of prior CAR T-cell immunotherapies.

196. Antibodies to Vaccine-preventable Infections After CAR-T Cell Immunotherapy for B Cell Malignancies

Background

Chimeric antigen receptor-modified T (CAR-T) cell immunotherapy for B cell hematologic malignancies results in prolonged B cell depletion. Little is known about the effects of CAR-T cell therapy on pre-existing pathogen-specific humoral immunity.

Methods

We conducted a prospective, cross-sectional study of children and adults treated with CD19- or BCMA-CAR-T cell therapy. Eligible patients were ≥ 6 months post-CAR-T cell infusion and in remission without subsequent chemoimmunotherapy. We measured total immunoglobulin G (IgG), pathogen-specific IgG levels for 12 vaccine-preventable infections, and B cell subsets from blood. Seroprotective antibody titers were based on standard thresholds. We described the proportion of patients with seroprotective titers and tested for associations between clinical factors and seroprotection using generalized estimating equations.

Results

We enrolled 65 patients who received CD19- (n=54) or BCMA- (n=11) CAR-T cell therapy. Seven patients were < 18 years old. Samples were collected a median of 20 months (range, 7–68) after CAR T cell infusion. Seroprotection to vaccine-preventable pathogens was generally comparable to the U.S. population (Fig 1) even though blood CD19+ B cell counts were low (< 20 cells/mm3) in 60% of patients. Among 30 patients without IgG replacement in the prior 16 weeks (4 half-lives of IgG), 27 (90%) had hypogammaglobulinemia. Despite this, these individuals had seroprotection to a median of 67% (IQR, 59%-73%) of tested pathogens (Fig 2A). The proportion of patients with seroprotection was lowest for mumps, hepatitis A and B, H. influenzae type B (Hib), S. pneumoniae, and B. pertussis. Patients receiving BCMA-CAR-T cells had seroprotection to fewer pathogens than those receiving CD19-CAR-T cells (Fig 2B), but the difference did not reach statistical significance (Fig 3). There were no significant differences by other variables.

Figure 1. Proportion of CAR-T cell recipients with seroprotection to vaccine-preventable infections compared to the U.S. population, stratified by receipt of IgG replacement in the previous 16 weeks.

Conclusion

Seroprotection for vaccine-preventable infections after CD19-CAR-T cell therapy was comparable to the general population. BCMA-CAR-T cell recipients may benefit most from replacement IgG. Vaccinations after CAR-T cell therapy should be considered and prioritized for S. pneumoniae, Hib, hepatitis viruses, and B. pertussis.

Disclosures

Justin J. Taylor, PhD, Vir Biotechnology (Grant/Research Support) Damian J. Green, MD, Cellectar Biosciences (Grant/Research Support)GSK (Advisor or Review Panel member)Juno Therapeutics (Grant/Research Support, Advisor or Review Panel member, Other Financial or Material Support, Royalities)Seattle Genetics (Grant/Research Support, Advisor or Review Panel member) Michael Boeckh, MD PhD, AlloVir (Consultant)EvrysBio (Advisor or Review Panel member, Other Financial or Material Support, share options)Gilead (Consultant, Grant/Research Support)GSK (Consultant)Helocyte (Advisor or Review Panel member, Shareholder)Lophius (Grant/Research Support)Merck (Consultant, Grant/Research Support)SymBio (Consultant)VirBio (Consultant, Grant/Research Support) David G. Maloney, MD, PhD, A2 Biotherapeutics (Consultant, Other Financial or Material Support, Stock Options)Bioline Rx (Consultant)Celgene (Consultant, Grant/Research Support)Gilead (Consultant)Juno Therapeutics (Consultant, Research Grant or Support, Other Financial or Material Support, four pending patents, not issued, licensed, no royalities, no licensees)Kite Pharma (Consultant, Grant/Research Support)Novartis (Consultant)Pharmacyclics (Consultant) Cameron J. Turtle, MBBS, PhD, Allogene (Other Financial or Material Support, Ad hoc advisory board (last 12 months))ArsenalBio (Advisor or Review Panel member, Other Financial or Material Support, Stock/options)AstraZeneca (Grant/Research Support, Other Financial or Material Support, Ad hoc advisory board (last 12 months))Caribou Biosciences (Advisor or Review Panel member, Other Financial or Material Support, Stock/options)Century Therapeutics (Advisor or Review Panel member)Eureka Therapeutics (Advisor or Review Panel member, Other Financial or Material Support, Stock/options)Juno Therapeutics (Grant/Research Support, Other Financial or Material Support, Patent: Licensed to Juno Therapeutics)Myeloid Therapeutics (Advisor or Review Panel member, Other Financial or Material Support, Stock/options)Nektar Therapeutics (Grant/Research Support, Other Financial or Material Support, Ad hoc advisory board (last 12 months))PACT Pharma (Other Financial or Material Support, Ad hoc advisory board (last 12 months))Precision Biosciences (Advisor or Review Panel member, Other Financial or Material Support, Stock/options)TCR2 Therapeutics (Grant/Research Support)T-CURX (Advisor or Review Panel member) Joshua A. Hill, MD, Allogene (Consultant)Allovir (Consultant)Gilead (Consultant)Karius (Grant/Research Support, Scientific Research Study Investigator)Takeda (Grant/Research Support, Scientific Research Study Investigator)

Detection of engineered T cells in FFPE tissue by multiplex in situ hybridization and immunohistochemistry

Identifying engineered T cells in situ is important to understand the location, persistence, and phenotype of these cells in patients after adoptive T cell therapy. While engineered cells are routinely characterized in fresh tissue or blood from patients by flow cytometry, it is difficult to distinguish them from endogenous cells in formalin-fixed, paraffin-embedded (FFPE) tissue biopsies. To overcome this limitation, we have developed a method for characterizing engineered T cells in fixed tissue using in situ hybridization (ISH) to the woodchuck hepatitis post-transcriptional regulatory element (WPRE) common in many lentiviral vectors used to transduce chimeric antigen receptor T (CAR-T) and T cell receptor T (TCR-T) cells, coupled with alternative permeabilization conditions that allows subsequent multiplex immunohistochemical (mIHC) staining within the same image. This new method provides the ability to mark the cells by ISH, and simultaneously stain for cell-associated proteins to immunophenotype CAR/TCR modified T cells within tumors, as well as assess potential roles of these cells in on-target/off-tumor toxicity in other tissue.

Society for Immunotherapy of Cancer (SITC) clinical practice guideline on immune effector cell-related adverse events

Immune effector cell (IEC) therapies offer durable and sustained remissions in significant numbers of patients with hematological cancers. While these unique immunotherapies have improved outcomes for pediatric and adult patients in a number of disease states, as 'living drugs,' their toxicity profiles, including cytokine release syndrome (CRS) and immune effector cell-associated neurotoxicity syndrome (ICANS), differ markedly from conventional cancer therapeutics. At the time of article preparation, the US Food and Drug Administration (FDA) has approved tisagenlecleucel, axicabtagene ciloleucel, and brexucabtagene autoleucel, all of which are IEC therapies based on genetically modified T cells engineered to express chimeric antigen receptors (CARs), and additional products are expected to reach marketing authorization soon and to enter clinical development in due course. As IEC therapies, especially CAR T cell therapies, enter more widespread clinical use, there is a need for clear, cohesive recommendations on toxicity management, motivating the Society for Immunotherapy of Cancer (SITC) to convene an expert panel to develop a clinical practice guideline. The panel discussed the recognition and management of common toxicities in the context of IEC treatment, including baseline laboratory parameters for monitoring, timing to onset, and pharmacological interventions, ultimately forming evidence- and consensus-based recommendations to assist medical professionals in decision-making and to improve outcomes for patients.

Cytokines in CAR T Cell-Associated Neurotoxicity

Chimeric antigen receptor (CAR) T cells provide new therapeutic options for patients with relapsed/refractory hematologic malignancies. However, neurotoxicity is a frequent, and potentially fatal, complication. The spectrum of manifestations ranges from delirium and language dysfunction to seizures, coma, and fatal cerebral edema. This novel syndrome has been designated immune effector cell-associated neurotoxicity syndrome (ICANS). In this review, we draw an arc from our current understanding of how systemic and potentially local cytokine release act on the CNS, toward possible preventive and therapeutic approaches. We systematically review reported correlations of secreted inflammatory mediators in the serum/plasma and cerebrospinal fluid with the risk of ICANS in patients receiving CAR T cell therapy. Possible pathophysiologic impacts on the CNS are covered in detail for the most promising candidate cytokines, including IL-1, IL-6, IL-15, and GM-CSF. To provide insight into possible final common pathways of CNS inflammation, we place ICANS into the context of other systemic inflammatory conditions that are associated with neurologic dysfunction, including sepsis-associated encephalopathy, cerebral malaria, thrombotic microangiopathy, CNS infections, and hepatic encephalopathy. We then review in detail what is known about systemic cytokine interaction with components of the neurovascular unit, including endothelial cells, pericytes, and astrocytes, and how microglia and neurons respond to systemic inflammatory challenges. Current therapeutic approaches, including corticosteroids and blockade of IL-1 and IL-6 signaling, are reviewed in the context of what is known about the role of cytokines in ICANS. Throughout, we point out gaps in knowledge and possible new approaches for the investigation of the mechanism, prevention, and treatment of ICANS.

Cytokine elevation in severe and critical COVID-19: a rapid systematic review, meta-analysis, and comparison with other inflammatory syndromes

The description of a so-called cytokine storm in patients with COVID-19 has prompted consideration of anti-cytokine therapies, particularly interleukin-6 antagonists. However, direct systematic comparisons of COVID-19 with other critical illnesses associated with elevated cytokine concentrations have not been reported. In this Rapid Review, we report the results of a systematic review and meta-analysis of COVID-19 studies published or posted as preprints between Nov 1, 2019, and April 14, 2020, in which interleukin-6 concentrations in patients with severe or critical disease were recorded. 25 COVID-19 studies (n=1245 patients) were ultimately included. Comparator groups included four trials each in sepsis (n=5320), cytokine release syndrome (n=72), and acute respiratory distress syndrome unrelated to COVID-19 (n=2767). In patients with severe or critical COVID-19, the pooled mean serum interleukin-6 concentration was 36·7 pg/mL (95% CI 21·6-62·3 pg/mL; I2=57·7%). Mean interleukin-6 concentrations were nearly 100 times higher in patients with cytokine release syndrome (3110·5 pg/mL, 632·3-15 302·9 pg/mL; p<0·0001), 27 times higher in patients with sepsis (983·6 pg/mL, 550·1-1758·4 pg/mL; p<0·0001), and 12 times higher in patients with acute respiratory distress syndrome unrelated to COVID-19 (460 pg/mL, 216·3-978·7 pg/mL; p<0·0001). Our findings question the role of a cytokine storm in COVID-19-induced organ dysfunction. Many questions remain about the immune features of COVID-19 and the potential role of anti-cytokine and immune-modulating treatments in patients with the disease.

Assessment and management of cytokine release syndrome and neurotoxicity following CD19 CAR-T cell therapy

Introduction: The success of CD19 chimeric antigen receptor (CAR)-T cell therapy for treatment of CD19 positive malignancies has led to the FDA approval of two CD19 CAR-T cell products, tisagenlecleucel and axicabtagene ciloleucel, and ongoing clinical trials of new products. Cytokine release syndrome (CRS) and neurotoxicity are common toxicities associated with CD19 CAR-T cell therapies.Areas covered: This review will discuss CRS and neurotoxicity associated with CD19 CAR-T cell therapies, including clinical presentation, risk factors, pathophysiology, and therapeutic or prophylactic interventions.Expert opinion: In conjunction with improved understanding of the pathophysiology of CRS and neurotoxicity, we expect that the recent development of consensus guidelines for the evaluation of these toxicities will enhance management of patients undergoing CD19 CAR-T cell therapies.

Value and affordability of CAR T-cell therapy in the United States

In the United States the increasing number of Food and Drug Administration (FDA)-approved, innovative, and potentially effective commercial cancer therapies pose a significant financial burden on public and private payers. Chimeric antigen receptor (CAR) T cells are prototypical of this challenge. In 2017 and 2018, tisagenlecleucel (Kymriah, Novartis) and axicabtagene ciloleucel (Yescarta, Kite) were approved by the FDA for use after showing groundbreaking results in relapsed/refractory B-cell malignancies. In 2020 and 2021, four further submissions to the FDA are expected for CAR T-cell therapies for indolent and aggressive B-cell malignancies and plasma cell myeloma. Yet, with marketed prices of over $350,000 per infusion for the two FDA-approved therapies and similar price tags expected for the coming products, serious concerns are raised over value and affordability. In this review we summarize recent, peer-reviewed cost-effectiveness studies of tisagenlecleucel and axicabtagene ciloleucel in the United States; discuss key issues concerning the health plan budget impact of CAR T-cell therapy; and review policy, payment and scientific approaches that may improve the value and affordability of CAR T-cell therapy.

Feasibility and efficacy of CD19-targeted CAR T cells with concurrent ibrutinib for CLL after ibrutinib failure

We previously reported durable responses in relapsed or refractory (R/R) chronic lymphocytic leukemia (CLL) patients treated with CD19-targeted chimeric antigen receptor-engineered (CD19 CAR) T-cell immunotherapy after ibrutinib failure. Because preclinical studies showed that ibrutinib could improve CAR T cell-antitumor efficacy and reduce cytokine release syndrome (CRS), we conducted a pilot study to evaluate the safety and feasibility of administering ibrutinib concurrently with CD19 CAR T-cell immunotherapy. Nineteen CLL patients were included. The median number of prior therapies was 5, and 17 patients (89%) had high-risk cytogenetics (17p deletion and/or complex karyotype). Ibrutinib was scheduled to begin ≥2 weeks before leukapheresis and continue for ≥3 months after CAR T-cell infusion. CD19 CAR T-cell therapy with concurrent ibrutinib was well tolerated; 13 patients (68%) received ibrutinib as planned without dose reduction. The 4-week overall response rate using 2018 International Workshop on CLL (iwCLL) criteria was 83%, and 61% achieved a minimal residual disease (MRD)-negative marrow response by IGH sequencing. In this subset, the 1-year overall survival and progression-free survival (PFS) probabilities were 86% and 59%, respectively. Compared with CLL patients treated with CAR T cells without ibrutinib, CAR T cells with concurrent ibrutinib were associated with lower CRS severity and lower serum concentrations of CRS-associated cytokines, despite equivalent in vivo CAR T-cell expansion. The 1-year PFS probabilities in all evaluable patients were 38% and 50% after CD19 CAR T-cell therapy, with and without concurrent ibrutinib, respectively (P = .91). CD19 CAR T cells with concurrent ibrutinib for R/R CLL were well tolerated, with low CRS severity, and led to high rates of MRD-negative response by IGH sequencing.

The chimeric antigen receptor-intensive care unit (CAR-ICU) initiative: Surveying intensive care unit practices in the management of CAR T-cell associated toxicities

PURPOSE

A task force of experts from 11 United States (US) centers, sought to describe practices for managing chimeric antigen receptor (CAR) T-cell toxicity in the intensive care unit (ICU).

MATERIALS AND METHODS

Between June-July 2019, a survey was electronically distributed to 11 centers. The survey addressed: CAR products, toxicities, targeted treatments, management practices and interventions in the ICU.

RESULTS

Most centers (82%) had experience with commercial and non-FDA approved CAR products. Criteria for ICU admission varied between centers for patients with Cytokine Release Syndrome (CRS) but were similar for Immune Effector Cell Associated Neurotoxicity Syndrome (ICANS). Practices for vasopressor support, neurotoxicity and electroencephalogram monitoring, use of prophylactic anti-epileptic drugs and tocilizumab were comparable. In contrast, fluid resuscitation, respiratory support, methods of surveillance and management of cerebral edema, use of corticosteroid and other anti-cytokine therapies varied between centers.

CONCLUSIONS

This survey identified areas of investigation that could improve outcomes in CAR T-cell recipients such as fluid and vasopressor selection in CRS, management of respiratory failure, and less common complications such as hemophagocytic lymphohistiocytosis, infections and stroke. The variability in specific treatments for CAR T-cell toxicities, needs to be considered when designing future outcome studies of critically ill CAR T-cell patients.

Clonal kinetics and single-cell transcriptional profiling of CAR-T cells in patients undergoing CD19 CAR-T immunotherapy

Chimeric antigen receptor (CAR) T-cell therapy has produced remarkable anti-tumor responses in patients with B-cell malignancies. However, clonal kinetics and transcriptional programs that regulate the fate of CAR-T cells after infusion remain poorly understood. Here we perform TCRB sequencing, integration site analysis, and single-cell RNA sequencing (scRNA-seq) to profile CD8+ CAR-T cells from infusion products (IPs) and blood of patients undergoing CD19 CAR-T immunotherapy. TCRB sequencing shows that clonal diversity of CAR-T cells is highest in the IPs and declines following infusion. We observe clones that display distinct patterns of clonal kinetics, making variable contributions to the CAR-T cell pool after infusion. Although integration site does not appear to be a key driver of clonal kinetics, scRNA-seq demonstrates that clones that expand after infusion mainly originate from infused clusters with higher expression of cytotoxicity and proliferation genes. Thus, we uncover transcriptional programs associated with CAR-T cell behavior after infusion.

Patient-Reported Neuropsychiatric Outcomes of Long-Term Survivors after Chimeric Antigen Receptor T Cell Therapy

CD19-targeted chimeric antigen receptor (CAR) modified T cell immunotherapy is a novel treatment with promising results in patients with relapsed/refractory lymphoid malignancies. CAR T cell therapy has known early toxicities of cytokine release syndrome and neurotoxicity, but little is known about long-term neuropsychiatric adverse effects. We have used patient-reported outcomes, including Patient-Reported Outcomes Measurement Information System (PROMIS) measures, to assess neuropsychiatric and other patient-reported outcomes of 40 patients with relapse/refractory chronic lymphocytic leukemia, non-Hodgkin lymphoma, and acute lymphoblastic leukemia 1 to 5 years after treatment with CD19-targeted CAR T cells. Mean T scores of PROMIS domains of global mental health, global physical health, social function, anxiety, depression, fatigue, pain, and sleep disturbance were not clinically meaningfully different from the mean in the general US population. However, 19 patients (47.5%) reported at least 1 cognitive difficulty and/or clinically meaningful depression and/or anxiety, and 7 patients (17.5%) scored ≤40 in global mental health, indicating at least 1 standard deviation worse than the general population mean. Younger age was associated with worse long-term global mental health (P = .02), anxiety (P = .001), and depression (P= .01). Anxiety before CAR T cell therapy was associated with increased likelihood of anxiety after CAR T cell therapy (P = .001). Fifteen patients (37.5%) reported cognitive difficulties after CAR T cell therapy. Depression before CAR T cell therapy was statistically significantly associated with higher likelihood of self-reported post-CAR T cognitive difficulties (P = .02), and there was a trend for an association between acute neurotoxicity and self-reported post-CAR T cognitive difficulties (P = .08). Having more post-CAR T cognitive difficulties was associated with worse global mental health and global physical health. Our study demonstrates overall good neuropsychiatric outcomes in 40 long-term survivors after CAR T cell therapy. However, nearly 50% of patients in the cohort reported at least 1 clinically meaningful negative neuropsychiatric outcome (anxiety, depression, or cognitive difficulty), indicating that a significant number of patients would likely benefit from mental health services following CAR T cell therapy. Younger age, pre-CAR T anxiety or depression, and acute neurotoxicity may be risk factors for long-term neuropsychiatric problems in this patient population. Larger studies are needed to confirm these findings.

Late Events after Treatment with CD19-Targeted Chimeric Antigen Receptor Modified T Cells

CD19-targeted chimeric antigen receptor-modified T cell (CAR-T cell) therapy has shown excellent antitumor activity in patients with relapsed/refractory B cell malignancies, with very encouraging response rates and outcomes. However, the late effects following this therapy remain unknown. Here we report late adverse events-defined as starting or persisting beyond 90 days after CAR-T cell infusion-in patients who survived at least 1 year after therapy. The median duration of follow-up was 28.1 months (range, 12.5 to 62.6 months). At last follow-up, 73% of patients were still alive and 24% were in ongoing complete remission (CR). The most common late adverse event was hypogammaglobulinemia (IgG <400 mg/dL or i.v immunoglobulinm (IVIG) replacement, observed in 67% of the patients with available data. Infection density was .55 infection/100 days at risk (2.08 per patient-year). The majority (80%) of the infections were treated in the outpatient setting, and 5% necessitated admission to the intensive care unit (ICU). Subsequent malignancies occurred in 15% of patients, including 5% with myelodysplastic syndrome (MDS). Among patients with ongoing CR and with no MDS, 16% experienced prolonged cytopenia requiring transfusions or growth factor support. Graft-versus-host disease occurred in 3 of 15 patients (20%) who had undergone previous allogeneic hematopoietic cell transplantation. Most of the late events observed in this cohort were not severe, and many could be related to previous or subsequent therapies, suggesting a safe long-term profile of CD19-targeted CAR-T cell immunotherapy.

Durable preservation of antiviral antibodies after CD19-directed chimeric antigen receptor T-cell immunotherapy

The long-term effects of CD19-targeted chimeric antigen receptor-modified T-cell immunotherapy (CD19-CARTx) for B-cell malignancies on humoral immunity are unclear. We examined antiviral humoral immunity in 39 adults with B-cell malignancies who achieved durable complete remission without additional therapy for >6 months after CD19-CARTx. Despite CD19+ B-cell aplasia in all patients, the incidence of viral infections occurring >90 days post-CD19-CARTx was low (0.91 infections per person-year). Because long-lived plasma cells are CD19- and should not be direct targets of CD19-targeted chimeric antigen receptor T cells, we tested the hypothesis that humoral immunity was preserved after CD19-CARTx based on linear mixed-effects models of changes in serum total immunoglobulin G (IgG) concentration, measles IgG concentration, and the number of viruses or viral epitopes to which serum IgG was directed (the "antivirome") using the novel VirScan assay. Samples were tested pre-CD19-CARTx and ∼1, 6, and 12 months post-CD19-CARTx. Although total IgG concentration was lower post-CD19-CARTx (mean change, -17.5%), measles IgG concentration was similar (mean change, 1.2%). Only 1 participant lost measles seroprotection post-CD19-CARTx but had undergone allogeneic hematopoietic cell transplantation before CD19-CARTx. The antivirome was also preserved, with mean absolute losses of 0.3 viruses and 6 viral epitopes detected between pre- and post-CD19-CARTx samples. Most participants gained IgG to ≥2 epitopes for ≥2 viruses, suggesting that humoral immunity to some viruses may be maintained or recover after successful CD19-CARTx. These findings may differ in children. Studies of immunoglobulin replacement and vaccination after CARTx are warranted.

High rate of durable complete remission in follicular lymphoma after CD19 CAR-T cell immunotherapy

Patients with follicular lymphoma (FL) with early relapse after initial chemoimmunotherapy, refractory disease, or histologic transformation (tFL) have limited progression-free and overall survival. We report efficacy and long-term follow-up of 21 patients with relapsed/refractory (R/R) FL (n = 8) and tFL (n = 13) treated on a phase 1/2 clinical trial with cyclophosphamide and fludarabine lymphodepletion followed by infusion of 2 × 106 CD19-directed chimeric antigen receptor-modified T (CAR-T) cells per kilogram. The complete remission (CR) rates by the Lugano criteria were 88% and 46% for patients with FL and tFL, respectively. All patients with FL who achieved CR remained in remission at a median follow-up of 24 months. The median duration of response for patients with tFL was 10.2 months at a median follow-up of 38 months. Cytokine release syndrome occurred in 50% and 39%, and neurotoxicity in 50% and 23% of patients with FL and tFL, respectively, with no severe adverse events (grade ≥3). No significant differences in CAR-T cell in vivo expansion/persistence were observed between FL and tFL patients. CD19 CAR-T cell immunotherapy is highly effective in adults with clinically aggressive R/R FL with or without transformation, with durable remission in a high proportion of FL patients. This trial was registered at clinicaltrials.gov as #NCT01865617.

Toxicities of CD19 CAR-T cell immunotherapy

CD19-targeted chimeric antigen receptor (CAR)-modified T (CAR-T) cell immunotherapy has demonstrated impressive results in B-cell malignancies, and CAR-T cell therapies targeting other antigens are in development for other cancers. Cytokine release syndrome (CRS) and neurotoxicity can be life-threatening in a subset of patients. The severity of CRS and neurotoxicity can be impacted by the disease burden, lymphodepletion regimen, and CAR-T cell dose. Tocilizumab and corticosteroids have been used to manage these toxicities, enabling CD19 CAR-T cells to be administered without obvious compromise in efficacy. Consensus criteria for grading and managing toxicities will facilitate the widespread application of this treatment modality.