Background: Treatment with Bortezomib (a proteasome inhibitor) and Daratumumab (DARA, a monoclonal anti CD38 antibody) are effective in patients with multiple myeloma (MM). However, these drugs impair cellular immunity, which may render the patients more prone to infection. Objective: To investigate the effect of Bortezomib-based regimens and Daratumumab monotherapy on the lymphocyte subpopulations in MM patients. Methods: Peripheral blood samples were collected from 32 patients, including 29 newly diagnosed who treated with bortezomib regimens and 3 patients with relapsed and refractory MM treated with Daratumumab as monotherapy. The immunophenotypic analysis was performed by flow cytometry at baseline and during the third cycle of Bortezomib regimen and fourth week of Daratumumab treatment. Results: In the third cycle of Bortezomib, there was a significant decrease in CD3+ T cells, CD+4 T cells, memory T cells, and natural killer cells (NK cells). However, CD8+ T cells increased dramatically, followed by a significant reduction in the CD4/CD8 ratio. On the other hand, Daratumumab led to an increase in the T cell population after four weeks of treatment, with a significant increase in CD3+ T cells as well as CD4+ T cells, while NK cells were dramatically depleted in all patients. Conclusion: Bortezomib had a negative influence on subsets of T cells, while Daratumumab positively affected T cells subsets. In both treatments, NK cells decreased significantly. These results suggested that DARA is more specific to target myeloma cells than Bortezomib. Also, DARA expanded T cells especially CD3+ T cells and CD4+ T cells.