PD-L1, LAG3, and HLA-DR are increasingly expressed during smoldering myeloma progression.

Symptomatic multiple myeloma (MM) is a plasma cell neoplasm that represents the final stage of a continuum of clinical conditions that start from monoclonal gammopathy of unknown significance (MGUS), then transits in the more advance, but still asymptomatic, smoldering MM (SMM), with a final evolution in symptomatic MM. To investigate SMM microenvironment modifications, we studied 16 patients diagnosed at our hospital. Eight of them (group A) developed MM within 2 years from diagnosis while the others (group B) had stable SMM. Samples were bone marrow biopsies at diagnosis and after 2 years (± 4 months) and were analyzed by immunohistochemical analysis. Firstly, we found a significant increase in both CD4+ cells (11 vs 17%, p < 0.01) and CD8+ cells (15 vs 18%, p < 0.01) between diagnosis and at follow-up samples (whole cohort). This was associated to an increase in the CD4+/CD8+ ratio (0.74 vs 0.93, p < 0.01). Secondly, we discovered an increased expression of T cell inhibitory molecules during SMM evolution. In fact, plasma cell PD-L1 and microenvironment cell LAG3 expression increased from 1 to 12% (p = 0.03) and 4 to 10% (p = 0.04), respectively, from diagnosis to follow-up. Also, plasma cells and microenvironment cells HLA-DR expression augmented during SMM evolution from 7 to 10% (p = 0.04) and 29 to 39% (p = 0.01), respectively. When comparing group A vs group B, we found an increased CD68-KP1+ cell infiltration in favor of group B at diagnosis (23 vs 28%, p = 0.01) and a greater plasma cell infiltration at follow-up (50 vs 26%, p < 0.01). Our findings suggest how immune escape mechanisms appear earlier during multiple myeloma evolution, and that LAG3 could be a possible immunologic target in this setting.