Antisense targeting of FOXP3+ Tregs to boost anti-tumor immunity

Akimova et al., Frontiers in Immunology, 2024 asked whether the regulatory T cells inside a tumor can be disabled while the regulatory T cells that keep the rest of the immune system in balance are left alone. The target was FOXP3, the transcription factor that defines a regulatory T cell and for which no unique surface marker exists. Nineteen AUMsilence sdASOs were designed against different regions of FOXP3 and screened at 1.5 μM in stimulated peripheral blood mononuclear cells from healthy donors; 11 of the 19 passed criteria for knockdown, viability and T cell division. AUM BioTech developed, produced and supplied the oligonucleotides, and three of the authors are from AUM BioTech.

In human material the sdASOs lowered FOXP3 messenger RNA by 54.9% in peripheral blood mononuclear cells and by 64.7% in cancer samples, with matching falls of 41.0% and 60.0% in regulatory T cell numbers, all at p<0.0001, and with no effect on the other FOXP family genes. Isolated human regulatory T cells needed only 3.5 hours at 2.5 μM before their suppressive function fell to 66.4% of the Scramble control. The clinical material came from patients with lung cancer, mesothelioma and melanoma, and regulatory T cells taken from tumors, pleural effusions and draining lymph nodes responded more strongly than those from blood.

In mice, a murine sdASO called ASO 6B was given at 50 mg/kg intraperitoneally each day for 14 days from day 7 after tumor inoculation. Tumor growth slowed in both the TC1 and the MC38 model, 22% of TC1 tumors and 13.6% of MC38 tumors resorbed completely, and FOXP3 messenger RNA and regulatory T cell numbers fell inside the tumors while the draining lymph nodes and spleens were unchanged. The T cells remaining in the treated tumors carried fewer exhaustion markers and produced more perforin and granzyme B, and the authors report no histological sign of autoimmunity or inflammation.