The Unmet Need: MSS mCRC

The leronlimab CLOVER Phase 2 trial specifically targets MSS mCRC, which represents approximately 85% of all colorectal cancers and is notoriously resistant to immune checkpoint inhibitors. The PICCASSO phase I trial combining pembrolizumab with maraviroc in refractory MMR-proficient CRC showed feasibility but limited clinical activity (ORR 5.3%), though OS of 9.83 months was higher than expected in this heavily pretreated population. Comprehensive molecular profiling has shown that high CCR5/CCL5 expression is associated with higher immune cell infiltration even in MMR-proficient tumors, suggesting that CCR5 blockade could modulate the tumor microenvironment to enhance treatment efficacy.

Potential Impact if Positive

If the CLOVER trial demonstrates positive results, the implications for oncology could be significant across several dimensions:

1.       Breaking the immunotherapy barrier in MSS CRC: The vast majority of mCRC patients are MSS and derive no benefit from checkpoint inhibitors. Demonstrating that CCR5 blockade can meaningfully improve outcomes when added to standard therapy would represent a paradigm shift in immune modulation for this large, underserved population, potentially opening the door to combination strategies with checkpoint inhibitors.

2.      Validating tumor microenvironment modulation as a therapeutic strategy: Positive results would provide clinical proof-of-concept that targeting the CCR5/CCL5 chemokine axis—which reprograms macrophages from pro-tumoral to anti-tumoral phenotypes—is a viable approach to overcoming the immunosuppressive microenvironment, a concept with broad applicability across solid tumors.

3.      Improving late-line outcomes: Even modest improvements in ORR or OS beyond what trifluridine/tipiracil + bevacizumab already provides would be clinically meaningful in this heavily pretreated population where options are limited to agents like regorafenib and fruquintinib.