Both Intermittent and Continuous Dosing Regimens Of Pomalidomide Mediate Broad Activation Of Innate and Adaptive Immunity In Relapsed/Refractory Myeloma: Results Of A Phase II Randomized Trial

Pomalidomide (POM) is a novel IMiD® immunomodulatory agent with clinical activity in several settings including in relapsed / resistant myeloma (RRMM). Several preclinical studies have documented the immunologic effects of IMiD® immunomodulatory drugs. IMiD® now form the backbone of several emerging combination therapies in hematologic malignancies. In prior studies, the clinical activity of POM in relapsed myeloma has been demonstrated using both continuous and intermittent dosing regimens with and without steroids. However the impact of the specific POM dosing regimen and the effect of concurrent steroids (as commonly utilized in most combination regimens) on POM-induced immune activation in vivo is unknown. In order to evaluate these issues more directly, we analyzed samples from patients enrolled in a randomized phase II clinical trial comparing two POM dosing schedules. Comparison of drug-induced immune activation between the two dosing schedules was one of the pre-specified endpoints in this study. Patients (n=39) with RRMM documented to be refractory to lenalidomide were randomized to therapy with POM 2 mg/day for 28/28 days (Arm A, n=19) or POM 4 mg/day for 21/28 days (Arm B, n=20) of a 28 day cycle. All patients (pts) received POM alone for cycle 1, followed by the addition of dexamethasone (DEX) at 40 mg weekly in subsequent cycles in both arms. In recent studies, we have shown that immune effects of lenalidomide are manifest early, within a week of initiation of therapy (Richter et al, Blood 121:423, 2013). Therefore each patient was analyzed 1 week after initiation of POM alone at 2 or 4 mg (cycle 1) or POM + DEX (cycle 2). POM therapy led to an increase in T cells at day 7 after initiation of therapy (mean percent increase compared to baseline 47%, p <0.01). This POM-induced T cell expansion consisted predominantly of CD8+ T cells (mean increase compared to baseline 40%, p<0.01). POM therapy also led to an increase in circulating natural killer (NK) cells (mean increase compared to baseline 92%, p<0.01) which peaked at 7 days post-initiation of therapy. POM-induced NK expansion was associated with an increase in the expression of NKG2D as well as CD16 and CD56, consistent with NK activation in vivo. Changes in T and NK cells following cycle 2 (POM+DEX) were compared with the data on cycle 1 (POM alone) in the same patient to evaluate the impact of DEX. Addition of DEX led to dampening of drug-induced T cell activation in vivo, but surprisingly did not dampen drug induced NK activation. Comparison of data from the two cohorts demonstrated that both 2 mg and 4 mg dose of POM led to comparable degree of immune activation in vivo, particularly for NK cells. In selected patients, post-treatment bone marrow samples were available after completion of at least 2 cycles of therapy. Comparison of the transcriptome of the CD138-depleted fraction from these marrows (representing bulk tumor microenvironment) identified nearly 300 genes upregulated in the bone marrow microenvironment post therapy compared to paired baseline samples. Interestingly, these genes were highly enriched in genes associated with T and NK activation. As POM led to activation of both innate and adaptive immunity, we also analyzed drug-induced changes in the myeloid compartment. Comparison of gene expression profiles (GEP) of purified CD14+ monocytes before and after POM indicated that POM therapy leads to a distinct GEP signature in myeloid cells in vivo. Finally, correlation of drug-induced changes in immune cells with clinical response demonstrated that an increase in post-therapy T cells correlated with clinical response, but post-treatment increase in NK cells did not. Together these data demonstrate that both 2 mg and 4 mg dose of POM can mediate broad activation of both innate and adaptive immunity in vivo, even in the setting of immune paresis associated with advanced, heavily pre-treated disease. Both continuous and intermittent dosing schedules of POM have comparable pharmacodynamic effects on immune activation. POM-induced immune activation is detected even with concurrent steroids and immune-related genes constitute a dominant component of drug induced changes in tumor microenvironment. POM-mediated immune activation may thus be exploited in the context of combination with immune therapies as well as monoclonal antibodies.