Chimeric antigen receptor-T-cell therapies going viral: latent and incidental viral infections.

PURPOSE OF REVIEW: Infections are the leading cause of non-relapse mortality following chimeric antigen receptor (CAR)-T-cell therapy, with viral infections being frequent both in the early and late phases post-infusion. We review the epidemiology of viral infections and discuss critical approaches to prevention and management strategies in this setting. RECENT FINDINGS: Herpesviruses dominate the early period. herpes simplex virus and varicella zoster virus infections are rare due to widespread antiviral prophylaxis, but cytomegalovirus (CMV) reactivation is increasingly observed, particularly in high-risk groups including B cell maturation antigen (BCMA)-CAR-T-cell therapy recipients and patients receiving corticosteroids. While CMV end-organ disease is rare, CMV is associated with increased mortality, emphasizing the need to evaluate the broader impact of CMV on long-term hematological, infection, and survival outcomes. Human herpesvirus-6 (HHV-6) has also emerged as a concern, with its diagnosis complicated by overlapping symptoms with neurotoxicity, underscoring the importance of considering viral encephalitis in differential diagnoses. Respiratory viruses are the most common late infections with a higher incidence after BCMA CAR-T-cell therapy. Vaccination remains a critical preventive measure against respiratory viruses but may be less immunogenic following CAR-T-cell therapy. The optimal timing, type of vaccine, and dosing schedule require further investigation. SUMMARY: A better understanding of viral epidemiology and preventive trials are needed to improve infection prevention practices and outcomes following CAR-T-cell therapies.

A systematic review and meta-analysis of HHV-6 and mortality after hematopoietic cell transplant.

Human herpesvirus-6B (HHV-6B) reactivation has been associated with non-relapse mortality (NRM) and overall mortality (OM) following allogeneic hematopoietic stem cell transplant (HCT). We performed a systematic review and meta-analysis to better quantify the association. Studies were included if they systematically tested a cohort of HCT recipients for HHV-6 infection or reactivation and described mortality for patients with and without HHV-6B. Random effects models were used to assess the pooled effect of HHV-6B positivity on each outcome of interest. Bayesian aggregation was additionally performed if models included 10 or fewer studies. Eight studies were included in the NRM analysis, which demonstrated a significant association between HHV-6 detection and NRM (pooled effect: 1.84; 95% CI: 1.29-2.62) without significant heterogeneity (I2 = 0.0%, p = 0.55). A Bayesian aggregation of the raw data used to construct the NRM random effects model supported these findings (95% credible interval: 0.15-1.13). Twenty-five studies were included in OM analysis, which showed a significant positive association (pooled effect: 1.37; 95% CI: 1.07-1.76), though considerable heterogeneity was observed (I2 = 36.7%, p < 0.05). HHV-6 detection is associated with NRM and OM following HCT. Randomized trials are warranted to evaluate if preventing or treating HHV-6B reactivation improves outcomes.

COVID-19 Outcomes Among Hematopoietic Cell Transplant and Chimeric Antigen Receptor T-Cell Recipients in the Era of SARS-CoV-2 Omicron Variants and COVID-19 Therapeutics.

Recipients of cellular therapies, including hematopoietic cell transplant (HCT) and chimeric antigen receptor T-cell (CART) therapy, are at risk for poor outcomes from coronavirus disease 2019 (COVID-19). There are limited data describing outcomes among patients in the pre- and early post-cellular therapy period during the Omicron era when multiple antiviral therapeutics were widely available. The objective of this study is to describe COVID-19 treatment and outcomes in patients diagnosed with COVID-19 during the pre- or early post-cellular therapy period. This is a single-center retrospective cohort study of adult HCT and CART recipients diagnosed with COVID-19 in the pre- and early post-cellular therapy period who tested positive for COVID-19 at our cancer center between January 1, 2022 and March 1, 2023. Primary outcomes were 30-day COVID-19-related hospitalization and death. A secondary outcome was development of persistent COVID-19, defined by a positive SARS-CoV-2 polymerase chain reaction (PCR) 31 to 90 days after COVID-19 diagnosis. Among 65 patients included, 52 (80%) received at least one COVID-19 therapeutic. The most common treatment after initial COVID-19 diagnosis was nirmatrelvir/ritonavir (29%), followed by monoclonal antibody therapy (26%) and remdesivir (11%). Of the 64 patients with at least 30 days of follow-up, 8 (12%) had at least one COVID-19-related hospitalization and one patient died, though cause of death was not due to COVID-19. Of the 8 patients hospitalized for COVID-19, one had severe disease and 7 had mild or moderate infection. Persistent COVID-19 was observed in 13/65 (20%) patients, with 4 patients requiring additional antiviral therapy. Three pre-cellular therapy patients had delays in receiving cellular therapy due to persistent COVID-19. During the Omicron era, rates of 30-day COVID-19-related hospitalization and death were relatively low in this cohort of pre- and early post-HCT and CART recipients, the majority of whom received treatment with at least one antiviral agent. Persistent COVID-19 occurred in 1 in 5 patients in the peri-cellular therapy period and led to cellular therapy treatment delays in several patients, highlighting the need for new COVID-19 treatment strategies.

Clinical Utility of Plasma Microbial Cell-Free DNA Sequencing Among Immunocompromised Patients With Pneumonia.

Background: Plasma microbial cell-free DNA (mcfDNA) sequencing can establish the etiology of multiple infectious syndromes by identifying microbial DNA in plasma. However, data are needed to define the clinical scenarios where this tool offers the highest clinical benefit. Methods: We conducted a prospective multicenter observational study that evaluated the impact of plasma mcfDNA sequencing compared with usual care testing among adults with hematologic malignancies. This is a secondary analysis of an expanded cohort that evaluated the clinical utility of plasma mcfDNA sequencing across prespecified and adjudicated outcomes. We examined the percentage of participants for whom plasma mcfDNA sequencing identified a probable cause of pneumonia or clinically relevant nonpneumonia infection. We then assessed potential changes in antimicrobial therapy based on plasma mcfDNA sequencing results and the potential for early mcfDNA testing to avoid bronchoscopy and its associated adverse events. Results: Of 223 participants, at least 1 microbial detection by plasma mcfDNA sequencing was adjudicated as a probable cause of pneumonia in 57 (25.6%) and a clinically relevant nonpneumonia infection in 88 (39.5%). A probable cause of pneumonia was exclusively identified by plasma mcfDNA sequencing in 23 (10.3%) participants. Antimicrobial therapy would have changed for 41 (18.4%) participants had plasma mcfDNA results been available in real time. Among the 57 participants with a probable cause of pneumonia identified by plasma mcfDNA sequencing, bronchoscopy identified no additional probable cause of pneumonia in 52 (91.2%). Conclusions: Plasma mcfDNA sequencing could improve management of both pneumonia and other concurrent infections in immunocompromised patients with suspected pneumonia.

Best Practice Considerations by The American Society of Transplant and Cellular Therapy: Infection Prevention and Management After Chimeric Antigen Receptor T Cell Therapy for Hematological Malignancies.

Chimeric antigen receptor (CAR) T-cell therapy is rapidly advancing, offering promising treatments for patients with hematological malignancy. However, associated infectious complications remain a significant concern because of their contribution to patient morbidity and non-relapse mortality. Recent epidemiological insights shed light on risk factors for infections after CAR T-cell therapy. However, the available evidence is predominantly retrospective, highlighting a need for further prospective studies. Institutions are challenged with managing infections after CAR T-cell therapy but variations in the approaches taken underscore the importance of standardizing infection prevention and management protocols across different healthcare settings. Therefore, the Infectious Diseases Special Interest Group of the American Society of Transplantation and Cellular Therapy assembled an expert panel to develop best practice considerations. The aim was to guide healthcare professionals in optimizing infection prevention and management for CAR T-cell therapy recipients and advocates for early consultation of Infectious Diseases during treatment planning phases given the complexities involved. By synthesizing current evidence and expert opinion these best practice considerations provide the basis for understanding infection risk after CAR T-cell therapies and propose risk-mitigating strategies in children, adolescents, and adults. Continued research and collaboration will be essential to refining and effectively implementing these recommendations.

CMV reactivation during pretransplantation evaluation: a novel risk factor for posttransplantation CMV reactivation.

ABSTRACT: Cytomegalovirus (CMV) disease occurs occasionally before allogeneic hematopoietic cell transplantation (HCT) and is associated with poor post-HCT outcomes; however, the impact of pre-HCT CMV reactivation is unknown. Pre-HCT CMV reactivation was assessed in HCT candidates from the preemptive antiviral therapy (2007-2017) and letermovir prophylaxis (2018-2021) eras. CMV DNA polymerase chain reaction (PCR) surveillance was routinely performed during the pre-HCT workup period, and antiviral therapy was recommended according to risk of progression to CMV disease. Risk factors for pre-HCT CMV reactivation were characterized, and the associations of pre-HCT CMV reactivation with post-HCT outcomes were examined using logistic regression and Cox proportional hazard models, respectively. A total of 1694 patients were identified, and 11% had pre-HCT CMV reactivation 14 days (median; interquartile range [IQR], 6-23) before HCT. Lymphopenia (≤0.3 × 103/µL) was the strongest risk factor for pre-HCT CMV reactivation at multiple PCR levels. In the preemptive therapy era, patients with pre-HCT CMV reactivation had a significantly increased risk of CMV reactivation by day 100 as well as CMV disease and death by 1 year after HCT. Clearance of pre-HCT CMV reactivation was associated with a lower risk of post-HCT CMV reactivation. Similar associations with post-HCT CMV end points were observed in a cohort of patients receiving letermovir prophylaxis. Pre-HCT CMV reactivation can be routinely detected in high-risk HCT candidates and is a significant risk factor for post-HCT CMV reactivation and disease. Pre-HCT CMV DNA PCR surveillance is recommended in high-risk HCT candidates, and antiviral therapy may be indicated to prevent post-HCT CMV reactivation.

How Immunocompromised Hosts Were Left Behind in the Quest to Control the COVID-19 Pandemic.

The immunocompromised population was disproportionately affected by the severe acute respiratory syndrome coronavirus 2 pandemic. However, these individuals were largely excluded from clinical trials of vaccines, monoclonal antibodies, and small molecule antivirals. Although the community of scientists, clinical researchers, and funding agencies have proven that these therapeutics can be made and tested in record time, extending this progress to vulnerable and medically complex individuals from the start has been a missed opportunity. Here, we advocate that it is paramount to plan for future pandemics by investing in specific clinical trial infrastructure for the immunocompromised population to be prepared when the need arises.

Human herpesvirus-6, HHV-8 and parvovirus B19 after allogeneic hematopoietic cell transplant: the lesser-known viral complications.

PURPOSE OF REVIEW: Viral infections continue to burden allogeneic hematopoietic cell transplant (HCT) recipients. We review the epidemiology, diagnosis, and management of human herpesvirus (HHV)-6, HHV-8 and parvovirus B19 following HCT. RECENT FINDINGS: Advances in HCT practices significantly improved outcomes but impact viral epidemiology: post-transplant cyclophosphamide for graft-versus-host disease prevention increases HHV-6 reactivation risk while the impact of letermovir for CMV prophylaxis - and resulting decrease in broad-spectrum antivirals - is more complex. Beyond the well established HHV-6 encephalitis, recent evidence implicates HHV-6 in pneumonitis. Novel less toxic therapeutic approaches (brincidofovir, virus-specific T-cells) may enable preventive strategies in the future. HHV-8 is the causal agent of Kaposi's sarcoma, which is only sporadically reported after HCT, but other manifestations are possible and not well elucidated. Parvovirus B19 can cause severe disease post-HCT, frequently manifesting with anemia, but can also be easily overlooked due to lack of routine screening and ambiguity of manifestations. SUMMARY: Studies should establish the contemporary epidemiology of HHV-6, and other more insidious viruses, such as HHV-8 and parvovirus B19 following HCT and should encompass novel cellular therapies. Standardized and readily available diagnostic methods are key to elucidate epidemiology and optimize preventive and therapeutic strategies to mitigate the burden of infection.

SARS-CoV-2 Vaccination in the First Year After Hematopoietic Cell Transplant or Chimeric Antigen Receptor T-Cell Therapy: A Prospective, Multicenter, Observational Study.

BACKGROUND: The optimal timing of vaccination with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccines after cellular therapy is incompletely understood. The objectives of this study are to determine whether humoral and cellular responses after SARS-CoV-2 vaccination differ if initiated <4 months versus 4-12 months after cellular therapy. METHODS: We conducted a multicenter, prospective, observational study at 30 cancer centers in the United States. SARS-CoV-2 vaccination was administered as part of routine care. We obtained blood prior to and after vaccinations at up to 5 time points and tested for SARS-CoV-2 spike (anti-S) IgG in all participants and neutralizing antibodies for Wuhan D614G, Delta B.1.617.2, and Omicron B.1.1.529 strains, as well as SARS-CoV-2-specific T-cell receptors, in a subgroup. RESULTS: We enrolled 466 allogeneic hematopoietic cell transplantation (HCT) (n = 231), autologous HCT (n = 170), and chimeric antigen receptor T-cell (CAR-T-cell) therapy (n = 65) recipients between April 2021 and June 2022. Humoral and cellular responses did not significantly differ among participants initiating vaccinations <4 months versus 4-12 months after cellular therapy. Anti-S IgG ≥2500 U/mL was correlated with high neutralizing antibody titers and attained by the last time point in 70%, 69%, and 34% of allogeneic HCT, autologous HCT, and CAR-T-cell recipients, respectively. SARS-CoV-2-specific T-cell responses were attained in 57%, 83%, and 58%, respectively. Pre-cellular therapy SARS-CoV-2 infection or vaccination and baseline B-cell count were key predictors of post-cellular therapy immunity. CONCLUSIONS: These data support mRNA SARS-CoV-2 vaccination prior to, and reinitiation 3 to 4 months after, cellular therapies with allogeneic HCT, autologous HCT, and CAR-T-cell therapy.

Unveiling the proteome-wide autoreactome enables enhanced evaluation of emerging CAR T cell therapies in autoimmunity.

Given the global surge in autoimmune diseases, it is critical to evaluate emerging therapeutic interventions. Despite numerous new targeted immunomodulatory therapies, comprehensive approaches to apply and evaluate the effects of these treatments longitudinally are lacking. Here, we leveraged advances in programmable-phage immunoprecipitation methodology to explore the modulation, or lack thereof, of autoantibody profiles, proteome-wide, in both health and disease. Using a custom set of over 730,000 human-derived peptides, we demonstrated that each individual, regardless of disease state, possesses a distinct and complex constellation of autoreactive antibodies. For each individual, the set of resulting autoreactivites constituted a unique immunological fingerprint, or "autoreactome," that was remarkably stable over years. Using the autoreactome as a primary output, we evaluated the relative effectiveness of various immunomodulatory therapies in altering autoantibody repertoires. We found that therapies targeting B cell maturation antigen (BCMA) profoundly altered an individual's autoreactome, while anti-CD19 and anti-CD20 therapies had minimal effects. These data both confirm that the autoreactome comprises autoantibodies secreted by plasma cells and strongly suggest that BCMA or other plasma cell-targeting therapies may be highly effective in treating currently refractory autoantibody-mediated diseases.

Human herpesvirus 6 reactivation and disease are infrequent in chimeric antigen receptor T-cell therapy recipients.

ABSTRACT: Human herpesvirus 6B (HHV-6B) reactivation and disease are increasingly reported after chimeric antigen receptor (CAR) T-cell therapy (CARTx). HHV-6 reactivation in the CAR T-cell product was recently reported, raising questions about product and patient management. Because of overlapping manifestations with immune effector cell-associated neurotoxicity syndrome, diagnosing HHV-6B encephalitis is challenging. We provide 2 lines of evidence assessing the incidence and outcomes of HHV-6B after CARTx. First, in a prospective study with weekly HHV-6B testing for up to 12 weeks after infusion, HHV-6B reactivation occurred in 8 of 89 participants; 3 had chromosomally integrated HHV-6 and were excluded, resulting in a cumulative incidence of HHV-6B reactivation of 6% (95% confidence interval [CI], 2.2-12.5). HHV-6B detection was low level (median peak, 435 copies per mL; interquartile range, 164-979) and did not require therapy. Second, we retrospectively analyzed HHV-6B detection in the blood and/or cerebrospinal fluid (CSF) within 12 weeks after infusion in CARTx recipients. Of 626 patients, 24 had symptom-driven plasma testing, with detection in 1. Among 34 patients with CSF HHV-6 testing, 1 patient had possible HHV-6 encephalitis for a cumulative incidence of 0.17% (95% CI, 0.02-0.94), although symptoms improved without treatment. Our data demonstrate that HHV-6B reactivation and disease are infrequent after CARTx. Routine HHV-6 monitoring is not warranted.

Final outcomes from a phase 2 trial of posoleucel in allogeneic hematopoietic cell transplant recipients.

ABSTRACT: Allogeneic hematopoietic cell transplantation (allo-HCT) recipients are susceptible to viral infections. We conducted a phase 2 trial evaluating the safety and rate of clinically significant infections (CSIs; viremia requiring treatment or end-organ disease) after infusion of posoleucel, a partially HLA-matched, allogeneic, off-the-shelf, multivirus-specific T-cell investigational product for preventing CSIs with adenovirus, BK virus, cytomegalovirus, Epstein-Barr virus, human herpesvirus-6, or JC virus. This open-label trial enrolled allo-HCT recipients at high risk based on receiving grafts from umbilical cord blood, haploidentical, mismatched, or matched unrelated donors; post-HCT lymphocytes of <180/mm3; or use of T-cell depletion. Posoleucel dosing was initiated within 15 to 49 days of allo-HCT and subsequently every 14 days for up to 7 doses. The primary end point was the number of CSIs due to the 6 target viruses by week 14. Of the 26 patients enrolled, only 3 (12%) had a CSI by week 14, each with a single target virus. In vivo expansion of functional virus-specific T cells detected via interferon-γ enzyme-linked immunosorbent spot assay was associated with viral control. Persistence of posoleucel-derived T-cell clones for up to 14 weeks after the last infusion was confirmed by T-cell-receptor deep sequencing. Five patients (19%) had acute graft-versus-host disease grade 2 to 4. No patient experienced cytokine release syndrome. All 6 deaths were due to relapse or disease progression. allo-HCT recipients at high risk who received posoleucel had low rates of CSIs from 6 targeted viruses. Repeat posoleucel dosing was generally safe and well tolerated and associated with functional immune reconstitution. This trial was registered at www.ClinicalTrials.gov as #NCT04693637.

Human Herpes Virus-6 (HHV-6) Reactivation after Hematopoietic Cell Transplant and Chimeric Antigen Receptor (CAR)- T Cell Therapy: A Shifting Landscape.

HHV-6B reactivation affects approximately half of all allogeneic hematopoietic cell transplant (HCT) recipients. HHV-6B is the most frequent infectious cause of encephalitis following HCT and is associated with pleiotropic manifestations in this setting, including graft-versus-host disease, myelosuppression, pneumonitis, and CMV reactivation, although the causal link is not always clear. When the virus inserts its genome in chromosomes of germ cells, the chromosomally integrated form (ciHHV6) is inherited by offspring. The condition of ciHHV6 is characterized by the persistent detection of HHV-6 DNA, often confounding diagnosis of reactivation and disease-this has also been associated with adverse outcomes. Recent changes in clinical practice in the field of cellular therapies, including a wider use of post-HCT cyclophosphamide, the advent of letermovir for CMV prophylaxis, and the rapid expansion of novel cellular therapies require contemporary epidemiological studies to determine the pathogenic role and spectrum of disease of HHV-6B in the current era. Research into the epidemiology and clinical significance of HHV-6B in chimeric antigen receptor T cell (CAR-T cell) therapy recipients is in its infancy. No controlled trials have determined the optimal treatment for HHV-6B. Treatment is reserved for end-organ disease, and the choice of antiviral agent is influenced by expected toxicities. Virus-specific T cells may provide a novel, less toxic therapeutic modality but is more logistically challenging. Preventive strategies are hindered by the high toxicity of current antivirals. Ongoing study is needed to keep up with the evolving epidemiology and impact of HHV-6 in diverse and expanding immunocompromised patient populations.

Defining and Grading Infections in Clinical Trials Involving Hematopoietic Cell Transplantation: A Report From the BMT CTN Infectious Disease Technical Committee.

The Blood and Marrow Transplant Clinical Trials Network (BMT-CTN) was established in 2001 to conduct large multi-institutional clinical trials addressing important issues towards improving the outcomes of HCT and other cellular therapies. Trials conducted by the network investigating new advances in HCT and cellular therapy not only assess efficacy but require careful capturing and severity assessment of adverse events and toxicities. Adverse infectious events in cancer clinical trials are typically graded according to the National Cancer Institute's Common Terminology Criteria for Adverse Events (CTCAE). However, there are limitations to this framework as it relates to HCT given the associated immunodeficiency and delayed immune reconstitution. The BMT-CTN Infection Grading System is a monitoring tool developed by the BMT CTN to capture and monitor infectious complications and differs from the CTCAE by its classification of infections based on their potential impact on morbidity and mortality for HCT recipients. Here we offer a report from the BMT CTN Infectious Disease Technical Committee regarding the rationale, development, and revising of BMT-CTN Infection Grading System and future directions as it applies to future clinical trials involving HCT and cellular therapy recipients.

Outcomes in Hematopoietic Cell Transplant and Chimeric Antigen Receptor T-Cell Therapy Recipients With Pre-Cellular Therapy SARS-CoV-2 Infection.

BACKGROUND: Hematopoietic cell transplant (HCT) or chimeric antigen receptor (CAR) T-cell therapy recipients have high morbidity from severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. There are limited data on outcomes from SARS-CoV-2 infection shortly before cellular therapy and uncertainty whether to delay therapy. METHODS: We conducted a retrospective cohort study of patients with SARS-CoV-2 infection within 90 days before HCT or CAR-T-cell therapy between January 2020 and November 2022. We characterized the kinetics of SARS-CoV-2 detection, clinical outcomes following cellular therapy, and impact on delays in cellular therapy. RESULTS: We identified 37 patients (n = 15 allogeneic HCT, n = 11 autologous HCT, n = 11 CAR-T-cell therapy) with SARS-CoV-2 infections within 90 days of cellular therapy. Most infections (73%) occurred between March and November 2022, when Omicron strains were prevalent. Most patients had asymptomatic (27%) or mild (68%) coronavirus disease 2019 (COVID-19). SARS-CoV-2 positivity lasted a median of 20.0 days (interquartile range, 12.5-26.25 days). The median time from first positive SARS-CoV-2 test to cellular therapy was 45 days (interquartile range, 37.75-70 days); 1 patient tested positive on the day of infusion. After cellular therapy, no patients had recrudescent SARS-CoV-2 infection or COVID-19-related complications. Cellular therapy delays related to SARS-CoV-2 infection occurred in 70% of patients for a median of 37 days. Delays were more common after allogeneic (73%) and autologous (91%) HCT compared to CAR-T-cell therapy (45%). CONCLUSIONS: Patients with asymptomatic or mild COVID-19 may not require prolonged delays in cellular therapy in the context of contemporary circulating variants and availability of antiviral therapies.

SARS-CoV-2 vaccination in the first year after hematopoietic cell transplant or chimeric antigen receptor T cell therapy: A prospective, multicenter, observational study (BMT CTN 2101).

Background: The optimal timing of vaccination with SARS-CoV-2 vaccines after cellular therapy is incompletely understood. Objective: To describe humoral and cellular responses after SARS-CoV-2 vaccination initiated <4 months versus 4-12 months after cellular therapy. Design: Multicenter prospective observational study. Setting: 34 centers in the United States. Participants: 466 allogeneic hematopoietic cell transplant (HCT; n=231), autologous HCT (n=170), or chimeric antigen receptor T cell (CAR-T cell) therapy (n=65) recipients enrolled between April 2021 and June 2022. Interventions: SARS-CoV-2 vaccination as part of routine care. Measurements: We obtained blood prior to and after vaccinations at up to five time points and tested for SARS-CoV-2 spike (anti-S) IgG in all participants and neutralizing antibodies for Wuhan D614G, Delta B.1.617.2, and Omicron B.1.1.529 strains, as well as SARS-CoV-2-specific T cell receptors (TCRs), in a subgroup. Results: Anti-S IgG and neutralizing antibody responses increased with vaccination in HCT recipients irrespective of vaccine initiation timing but were unchanged in CAR-T cell recipients initiating vaccines within 4 months. Anti-S IgG ≥2,500 U/mL was correlated with high neutralizing antibody titers and attained by the last time point in 70%, 69%, and 34% of allogeneic HCT, autologous HCT, and CAR-T cell recipients, respectively. SARS-CoV-2-specific T cell responses were attained in 57%, 83%, and 58%, respectively. Humoral and cellular responses did not significantly differ among participants initiating vaccinations <4 months vs 4-12 months after cellular therapy. Pre-cellular therapy SARS-CoV-2 infection or vaccination were key predictors of post-cellular therapy anti-S IgG levels. Limitations: The majority of participants were adults and received mRNA vaccines. Conclusions: These data support starting mRNA SARS-CoV-2 vaccination three to four months after allogeneic HCT, autologous HCT, and CAR-T cell therapy. Funding: National Marrow Donor Program, Leukemia and Lymphoma Society, Multiple Myeloma Research Foundation, Novartis, LabCorp, American Society for Transplantation and Cellular Therapy, Adaptive Biotechnologies, and the National Institutes of Health.