Atypical Lymphocytosis Induced by T Cell-Engaging Therapy in Patients With Hematological Malignancies.

[INTRODUCTION] Atypical lymphocytes (ALYs) are activated lymphocytes with distinct morphological characteristics, often observed in various infections, autoimmune diseases, drug reactions, and malignancies. Their appearance may resemble leukemic or lymphoma cells, making it essential to differentiate ALYs, particularly in patients with hematological malignancies. With the advent of T-cell engagers (TCEs), a novel class of immuno-oncology drugs, this study aimed to investigate their effect on peripheral blood profiles, including ALYs.

[METHODS] We retrospectively analyzed complete blood count (CBC) data and peripheral blood morphology from 28 patients enrolled in clinical trials of various TCEs targeting multiple myeloma and B-cell lymphomas. The drugs studied included cevostamab, linvoseltamab, glofitamab, teclistamab, talquetamab, elranatamab, and epcoritamab.

[RESULTS] A transient increase in ALYs was observed in 11 of the 28 patients treated with TCEs. This was confirmed by changes in cell morphology and flow cytometric parameters obtained from the CBC analyzer. ALY elevation appeared to be influenced by drug type, administration route, and combination therapies. In addition, a sudden and transient decrease in both monocytes and lymphocytes was noted in peripheral blood following cevostamab treatment.

[CONCLUSION] The observed increase in ALYs likely reflects immune activation induced by TCEs. Understanding ALY dynamics during TCE treatment is crucial for clinicians and pathologists when interpreting patient test results. Furthermore, ALY testing may serve as a potential marker for predicting the effectiveness of TCE therapies.