Targeting endoglin-expressing regulatory T cells in the tumor microenvironment enhances the effect of PD1 checkpoint inhibitor immunotherapy

Purpose: Endoglin is a coreceptor for TGFb ligands that is highly expressed on proliferating endothelial cells and other cells in the tumor microenvironment. Clinical studies have noted increased programmed cell death (PD)-1 expression on cytotoxic T cells in the peripheral blood of patients with cancer treated with TRC105, an endoglin-targeting antibody. In this study, we investigated the combination of endoglin antibodies (TRC105 and M1043) with an anti-PD1 antibody.Experimental Design: The combination anti-endoglin/anti-PD1 antibodies was tested in four preclinical mouse models representing different stages of cancer development. To investigate the underlying mechanism, Fc-receptor-knockout mice were used complemented with depletion of multiple immune subsets in mice. Tumor growth and the composition of immune infiltrate were analyzed by flow cytometry. Finally, human colorectal cancer specimens were analyzed for presence of endoglin-expressing regulatory T cells (Treg).Results: In all models, the combination of endoglin antibody and PD1 inhibition produced durable tumor responses, leading to complete regressions in 30% to 40% of the mice. These effects were dependent on the presence of Fcg receptors, indicating the involvement of antibody-dependent cytotoxic responses and the presence of CD8(+) cytotoxic T cells and CD4(+) Th cells. Interestingly, treatment with the endoglin antibody, TRC105, significantly decreased the number of intratumoral Tregs. Endoglin-expressing Tregs were also detected in human colorectal cancer specimens.Conclusions: Taken together, these data provide a rationale for combining TRC105 and anti-PD1 therapy and provide additional evidence of endoglin's immunomodulatory role

Tumor Response After Neoadjuvant Magnetic Resonance Guided Single Ablative Dose Partial Breast Irradiation

Contains fulltext : 219916.pdf (Publisher’s version ) (Closed access)PURPOSE: To assess the pathologic and radiologic response in patients with low-risk breast cancer treated with magnetic resonance (MR) guided neoadjuvant partial breast irradiation (NA-PBI) and to evaluate toxicity and patient-reported outcomes (PROs). METHODS AND MATERIALS: For this single-arm prospective trial, women with unifocal, non-lobular tumors with a maximum diameter of 20 mm (age, 50-70 years) or 30 mm (age, >/=70 years) and tumor-negative sentinel node(s) were eligible. Patients were treated with a single ablative dose of NA-PBI followed by breast-conserving surgery after an interval of 6 to 8 months. Target volumes were defined on radiation therapy planning computed tomography scan and additional magnetic resonance imaging. Prescribed doses to gross tumor volume and clinical target volume (gross tumor volume plus 20 mm margin) were 20 Gy and 15 Gy, respectively. Primary outcome was pathologic complete response (pCR). Secondary outcomes were radiologic response (on magnetic resonance imaging), toxicity (Common Terminology Criteria for Adverse Events), PROs (European Organisation for Research and Treatment of Cancer QLQ-BR23, Hospital Anxiety and Depression Scale), and cosmesis (assessed by patient, radiation oncologist, and BCCT.core software). RESULTS: Thirty-six patients were treated with NA-PBI, and pCR was reported in 15 patients (42%; 95% confidence interval, 26%-59%). Radiologic complete response was observed in 15 patients, 10 of whom had pCR (positive predictive value, 67%; 95% confidence interval, 39%-87%). After a median follow-up of 21 months (range, 12-41), all patients experienced grade 1 fibrosis in the treated breast volume. Transient grade 2 and 3 toxicity was observed in 31% and 3% of patients, respectively. Local recurrences were absent. No deterioration in PROs or cosmetic results was observed. CONCLUSIONS: NA-PBI has the potential to induce pCR in a substantial proportion of patients, with acceptable toxicity. This treatment seems a feasible alternative to standard postoperative irradiation and could even result in postponement or omission of surgery if pCR can be accurately predicted in selected low-risk patients