CXCR4 Antagonism Reduces Pneumonia Severity in a Pharmacological Mouse Model of CXCR2 Loss-of-Function-Mediated Neutropenia Robert Johnson1, Arthur G. Taveras1, Jacob R. Bledsoe2, Chi Huu Nguyen3

1 X4 Pharmaceuticals Inc., Boston, MA, USA

2 Department of Pathology, Boston Children's Hospital, Harvard Medical School, Boston, MA

3X4 Pharmaceuticals (Austria) GmbH, Vienna, Austria

Character (no spaces): 3,793Introduction WHIM syndrome is a rare primary immunodeficiency disorder characterized by warts, hypogammaglobulinemia, frequent infections and myelokathexis with peripheral blood neutropenia and lymphopenia. Gain-of-function (GOF) variants in CXCR4 are recognized as the primary cause of WHIM syndrome1,2. Additionally, loss-of-function (LOF) variants in CXCR2 can lead to similar symptoms, including neutropenia, increased susceptibility to infections, and myelokathexis3,4. Mavorixafor, an oral CXCR4 antagonist, has demonstrated a clinical benefit that includes increased neutrophil count and concomitant reductions in infections for WHIM patients5. Recently, we developed a pharmacologically induced CXCR2 LOF mouse model that replicates pathogenic features observed in patients with CXCR2 LOF, including neutropenia, elevated neutrophil counts in bone marrow (BM), an increased myeloid-to-erythroid (M/E) ratio, and BM myelokathexis. Furthermore, our data indicated that a CXCR4 antagonist effectively alleviated circulating neutropenia, reversed BM neutrophil accumulation, normalized the M/E ratio, and decreased the frequency of myelokathexis in this model6. It remains unclear whether our CXCR2 LOF mouse model exhibits increased susceptibility to infections and whether the CXCR4 antagonist can effectively mitigate this susceptibility. The current study aims to address these critical questions.

Methods Female BALB/c mice (10-15 per group) were administered the CXCR2 antagonist navarixin (3 mg/kg) via oral gavage, followed by daily doses of the CXCR4 antagonist X4P-002 (10 mg/kg) or a vehicle control for 4 or up to 14 days, administered two hours after the navarixin dose. On day 1 post-treatment, the mice were inoculated with Streptococcus pneumoniae to induce pneumonia. Lung tissues were subsequently harvested to evaluate bacterial load and neutrophil counts, while monitoring mortality and overall survival throughout the study.

Results In addition to peripheral blood neutropenia, an elevated M/E ratio, and BM myelokathexis previously reported6, our pharmacologically induced CXCR2 LOF mice demonstrated increased susceptibility to pneumonia. This was evidenced by a significantly higher bacterial load in lung tissue homogenates, an increased mortality rate (46% in CXCR2 LOF mice compared to 23% in control mice on day 2 post infection), and reduced overall survival in CXCR2 LOF group. Notably, treatment with the CXCR4 antagonist effectively decreased bacterial load in lung tissues and lowered the mortality rate, as well as improved overall survival in CXCR2 LOF mice. Additionally, total neutrophil counts in lung tissue homogenates were significantly reduced in CXCR2 LOF mice which were restored with CXCR4 antagonism. These findings suggest that CXCR4 antagonism may normalize neutrophil infiltration into infected tissues, thereby enhancing bacterial clearance.

Conclusion Our CXCR2 LOF mice exhibit increased susceptibility to pneumonia, reflecting the clinical manifestations observed in patients with CXCR2 LOF. Notably, CXCR4 antagonism reduces the severity of pneumonia, likely associated with the normalization of neutrophil counts in infected tissues. In conjunction with our previous findings6, which showed that CXCR4 antagonism corrected blood and BM neutrophil abnormalities as well as reduced BM myelokathexis frequency, our data provide strong support for CXCR4 antagonist therapy as a promising treatment strategy for patients with CXCR2 LOF.

References:

  • Geier CB et al. J Clin Immunol. 2022;42(8):1748-1765.

  • Heusinkveld LE et al. J Clin Immunol. 2019;39(6):532-556.

  • Marin-Esteban V et al. Haematologica. 2022;107(3):765-769.

  • Auer PL, et al. Nat Genet. 2014;46(6):629-634.

  • Badolato R et al. Blood. 2024;144(1):35-45.

  • Nguyen CH et al. 2024; https://doi.org/10.1182/blood-2024-193174

Disclosures RJ, AT, and CHN are employees and/or shareholders of X4 Pharmaceuticals.

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2025
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