Antibody-mediated transient depletion of CD4+ cells enhances the expansion of tumor-reactive CD8+ T cells and exhibits robust antitumor effects in preclinical and clinical studies. To investigate the clonal T-cell responses following transient CD4+ cell depletion in patients with cancer, we conducted a temporal analysis of the T-cell receptor (TCR) repertoire in the first-in-human clinical trial of IT1208, a defucosylated humanized monoclonal anti-CD4. Transient depletion of CD4+ cells promoted replacement of T-cell clones among CD4+ and CD8+ T cells in the blood. This replacement of the TCR repertoire was associated with the extent of CD4+ T-cell depletion and an increase in CD8+ T-cell count in the blood. Next, we focused on T-cell clones overlapping between the blood and tumor in order to track tumor-associated T-cell clones in the blood. The total frequency of blood–tumor overlapping clones tended to increase in patients receiving a depleting dose of anti-CD4, which was accompanied by the replacement of overlapping clones. The greater expansion of CD8+ overlapping clones was commonly observed in the patients who achieved tumor shrinkage. These results suggested that the clonal replacement of the TCR repertoire induced by transient CD4+ cell depletion was accompanied by the expansion of tumor-reactive T-cell clones that mediated antitumor responses. Our findings propose beneficial remodeling of the TCR repertoire following transient CD4+ cell depletion and provide novel insight into the antitumor effects of monoclonal anti-CD4 treatment in patients with cancer.

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