Vaccines against SARS-CoV-2 have shown high efficacy, but immunocompromised participants were excluded from controlled clinical trials. We evaluated immune responses to the Pfizer/BioNTech mRNA vaccine in solid tumor patients (n=52) on active cytotoxic anti-cancer therapy. These responses were compared to a control cohort that also received the Pfizer/BioNTech vaccine (n=50). Using live SARS-CoV-2 assays, neutralizing antibodies were detected in 67% and 80% of cancer patients after the first and second immunizations, respectively, with a 3-fold increase in median titers after the booster. Similar trends were observed in serum antibodies against the receptor-binding domain (RBD) and S2 regions of Spike protein, and in IFN𝛾+ Spike-specific T cells. The magnitude of each of these responses was diminished relative to the control cohort. We therefore quantified RBD- and Spike S1-specific memory B cell subsets as predictors of anamnestic responses to viral exposures or additional immunizations. After the second vaccination, Spike-specific plasma cell-biased memory B cells were observed in most cancer patients at levels similar to those of the control cohort after the first immunization. These data suggest that a third immunization might elevate antibody responses in cancer patients to levels seen in healthy individuals after the second dose. Trials should be conducted to test these predictions.
Regulation of innate immune responses by DAI (DLM-1/ZBP1) and other DNA-sensing molecules
