In classical
hairy cell leukemia (HCL), standard treatments including
purine analogs achieve a durable response (up to 90%), but lead to severe immunosuppression and long-lasting depletion of CD4 + T lymphocytes. The BRAF inhibitor
vemurafenib is effective in HCL, but its use in first-line treatment is restricted to select clinical situations (e.g. active
infection). Its impact on immune function or response to
vaccines in HCL is unclear. We treated four HCL patients with
vemurafenib during the
COVID-19 pandemic and monitored immune reconstitution and response to SARS-CoV-2 immunization. All patients responded to HCL treatment with normalization of peripheral blood counts. No severe
infections occurred. As an indication of limited immunosuppression by
vemurafenib, stable CD4 + and CD8 + T lymphocyte counts and
immunoglobulin levels were observed. Three out of four patients received SARS-CoV-2 vaccination (Pfizer-BioNTech) during treatment with
vemurafenib.
IgG antibody levels against the spike-
protein of SARS-CoV-2 were detected (40-818 AE/ml). Our data suggest that
vemurafenib has limited effects on cellular and humoral immune function in HCL, which allows for successful SARS-CoV-2 vaccination. These data support the use of BRAF inhibitors during the current pandemic where continued immune response is necessary for minimizing the COVID-19-related risk of non-vaccinated patients.