Tu137 - Allogenic and Autologous Stem Cell Transplant (SCT) Recipients have Detectable Levels of SARS-CoV-2 Antigen-specific T Cells One Month After mRNA Vaccination

Introduction: The recent outbreak of SARS-CoV-2 has posed a serious threat to immune-compromised individuals. Concerns have been raised over the effectiveness of mRNA vaccinations in cancer patient populations. This small, cross-sectional study evaluates the ability of SARS-CoV-2 mRNA vaccines to elicit T cell responses in leukemia, lymphoma, and myeloma patients post-allo or auto-SCT.

Methodology: 7 allo- and auto-SCT recipients from the BC Cancer Agency were enrolled. Whole blood was collected at the time of SARS-CoV-2 vaccination (T1) and 3-4 weeks post dose 2 (T2). Antigen-induced marker assays were used to measure the magnitude of T cell responses overtime. Whole blood was stimulated for 48-hours in the presence of SARS-CoV-2 spike peptides at 37 C, and stained for CD25 and OX40 to measure CD4⁺ antigen-specific T cells and CD69 and CD137 to measure CD8⁺ antigen-specific T cells. Phenotyping of antigen-specific CD4⁺ T cells was conducted to measure the frequency of Tregs, Th1, Th1.17, Th2, Th9, and Th17 T cell subsets.

Results: All 7 individuals had detectable levels of antigen-specific CD4⁺ T cells at T2. 4 individuals (57%) had detectable levels of antigen-specific CD8⁺ T cells at T2. 4 individuals had sufficient antigen-specific CD4⁺ T cell frequencies to conduct phenotyping. The response skewed towards Th2, with 50.85% of antigen-specific CD4⁺ T cells being CCR4⁺ CCR6^-.

Conclusions: This promising preliminary data suggests allo- and auto-SCT recipients are capable of mounting antigen-specific T cell responses against the SARS-CoV-2 spike protein following mRNA vaccination. Additional timepoints are needed to evaluate the durability of this response.