The effect of mogamulizumab on the aberrant T cell population in the peripheral blood – A monocentric retrospective analysis

Summary Background and Objectives The effect of mogamulizumab in cutaneous T‐cell lymphoma (CTCL) on T cells (TC) in the peripheral blood and its potential role to navigate treatment intervals are explored. Methods We investigated within a retrospective monocentric analysis the effect of mogamulizumab on the CD3+ TC and the aberrant T cell population (TCP), i.e., the CD4+/CD7– and the CD4+/CD26– TC, analyzed by flow cytometry. Results Thirteen patients with CTCL were included. After four cycles there was a mean reduction of 57% in CD3+ TC, 72% in the CD4+/CD7– and 75% in the CD4+/CD26– TCP compared to the individual baseline of each patient. The reduction in CD4+/CD7+ and CD4+/CD26+ TC was lower, averaging 54% and 41%. A significant decrease in aberrant TCP was already evident after the first administration. A median plateau of TCP already occurred during the IP. Progressive disease occurred in 5/13 patients without a clear correlation to aberrant TCP. Conclusions Already after one dose of mogamulizumab, aberrant TCP and, to a lesser extent, normal TC decrease. We did not observe a clear correlation between TCP and the efficacy of mogamulizumab, but further studies with larger numbers of patients are needed.