Potential immune priming of the tumor microenvironment with FOLFOX chemotherapy in locally advanced rectal cancer.

Strategies to enhance tumor immunogenicity may expand the role of immunotherapy beyond the mismatch repair-deficient subtype. In this pilot study, biopsies were performed at baseline and after four cycles of FOLFOX in eight patients receiving neoadjuvant chemotherapy for stage II/III locally advanced rectal cancer. Immunostaining was performed for T cell subsets (CD3+, CD8+, CD45RO+); macrophages (CD163+); T regulatory cells (FOXP3+); and expression of MHC class I, PD-1 and PD-L1. Changes in cell number or intensity were quantified and correlated with treatment response. Pretreatment patterns of immune infiltrates were mixed and did not correlate with treatment response. Posttreatment increases in T cell infiltrates (CD3+, CD8+ and CD45RO+) and MHC-I expression were observed in five patients. CD163+ cell numbers increased in four patients. FOXP3+ cell numbers increased in two patients, decreased in two other patients and remained unchanged in three patients. PD-1 scores increased in seven patients, and PD-L1 scores increased in four patients. Changes in tumor T cell responses did not correlate with treatment response. Changes in FOXP3+ cells were associated with treatment response in some patients: two patients with increases in FOXP3+ cells had poor responses, whereas the patient with the greatest reduction in FOXP3+ cells had a complete response. The patient with a complete clinical response had a much higher increase in MHC-I expression than other patients. These results suggest that chemotherapy can increase immune activity in the tumor microenvironment and could potentially be utilized to prime immune responses prior to immunomodulatory treatments.