Effect of all-trans retinoic acid (ATRA) on differentiation of dendritic and immature myeloid cells in cancer patients

Proc Amer Assoc Cancer Res, Volume 47, 2006 4877 Abnormal differentiation of dendritic cells (DC) in cancer manifests in decreased presence and impaired function of mature DCs and the appearance of a larger number of immature myeloid cells (ImC) that are capable of suppressing antigen-specific T cells. Recently it becomes increasingly clear that success of immune intervention in cancer will depend on the ability to remove ImC and improve differentiation of DCs. Previous in vitro and in vivo studies in tumor-bearing mice suggested that all-trans-retinoic acid (ATRA) could improve DC differentiation and eliminate ImC. Here, we for the first time have tested the effect of ATRA on DCs and ImC in cancer patients. Eighteen patients with advanced stage renal cell carcinoma (RCC) were enrolled onto the study and received treatment with ATRA (50-150 mg/m2/day) for seven days. Seven days after completion of ATRA treatment patients started IL-2 therapy for five consecutive weeks. Peripheral blood was collected weekly. In parallel blood was collected from 16 patients that received IL-2 therapy alone. Control group comprised 7 healthy volunteers. Mononuclear cells (MNC) isolated at each time point were stored in liquid nitrogen. All samples from the same patient were analyzed simultaneously. After thawing MNC were cultured overnight and then were labeled with a cocktail of lineage specific antibodies (anti-CD3, CD19, CD56 and CD14), anti-HLA-DR antibody, anti-CD33 antibody, and either anti-CD86, anti-CD40, anti-CD83, or anti-CCR7 antibodies. ImC were defined as Lin negative, HLA-DR negative, CD33 positive cells. DCs were defined as lineage negative, HLA-DR positive cells. In addition, the presence of myeloid and plasmocytoid subsets of DCs was determined using anti-CD11c and anti-CD123 antibodies. Cells were evaluated by flow cytometry. The proportions of different populations of DCs were calculated. In addition the response of MNC to antigen (tetanus toxoid) and mitogen (PHA) was evaluated as well as the ability of DCs to stimulate allogeneic T cells. To date no adverse effect of the therapy was reported. This trial is at an early stage, however, the initial results are very encouraging. As expected almost all patients with metastatic RCC had increased level of ImC. ATRA treatment substantially decreased the number of ImC in more than 90% of them. In 60% of patients the presence of ImC was reduced to the control level. ATRA treatment substantially increased the proportion and functional activity of DCs. The presence of CD83+ or CD40+ mature DCs was also increased. These first results suggest that ATRA may substantially improve DC differentiation and eliminate ImC in cancer patients. It could be a valuable addition to different cancer immunotherapeutic strategies.