Allogeneic Engineered Red Blood Cells as an Anti-Tumor Therapeutic

Allogeneic engineered red blood cells as artificial antigen presenting cells interact with tumor-antigen specific T cells, drive memory formation, epitope spreading, and antitumor efficacy

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Checkpoint inhibitors and T-cell therapies have highlighted the critical role of T cells in anti-cancer immunity. However, limitations associated with these treatments, including significant toxicity and challenges with manufacturing, drive the need for alternative approaches to treat cancer.

At Rubius Therapeutics, we utilize the RED PLATFORM® to generate red blood cells (RBCs) and turn them into cellular medicines for the treatment of cancer and autoimmune diseases. These allogeneic Red Cell Therapeutics™ (RCTs) are derived from donor CD34+ hematopoietic progenitor cells that are genetically engineered and subsequently differentiated and matured into enucleated RBCs that express biotherapeutic proteins within or on their cell surface. This approach is designed to mimic human immunobiology through the cellular presentation of thousands of copies of biotherapeutic proteins on the surface of human enucleated RBCs.

RBCs have unique properties that make them attractive for allogeneic cell therapy. RBCs lack a nucleus and are unable to divide, O-negative RBCs are inherently biocompatible,1 and RBCs have a biodistribution limited to the blood vessels and spleen. Together these properties can limit the toxicities often associated with other immune boosting therapies in cancer.

Harnessing the RED PLATFORM, our team engineered RCTs into artificial antigen-presenting cells (aAPCs) to provide the optimal signals for effective T-cell activation. In this paper,2 we describe aAPCs comprised of a tumor-specific peptide bound to MHC class I, a costimulatory ligand (4-1BBL) and a cytokine signal, interleukin 12 (IL-12), thus providing the three signals needed for optimal T cell activation.

Using murine surrogate aAPCs that target a foreign model antigen or a tumor-associated antigen, we demonstrated effective tumor control, epitope spreading, and development of a responsive memory population upon multiple tumor rechallenges. Our aAPCs retained a favorable safety profile with minimal, reversible splenomegaly and liver inflammation. This is likely due to the biodistribution of the cells to the vasculature and spleen and the membrane-bound nature of 4-1BBL and IL-12, which limits its potential for on-target, off-tissue toxicities. We observed antigen-specific CD8+ T cell expansion and enhanced effector function. In addition, given the immune stimulatory effects of the 4-1BBL and IL-12 moieties on the cells, there were broad, target-antigen independent adaptive and innate immune responses that likely played a role in tumor control and epitope spreading.

Figure 1: RTX-321 Mechanism of Action

With these preclinical findings, we focused on engineering an aAPC, RTX-321, for the clinic to target human papillomavirus (HPV) 16, a high-risk strain of HPV, associated with various types of cancer, including cervical cancer, head and neck squamous cell carcinoma and anal cancer. RTX-321 expresses HLA-A*02:01 with HPV 16 E7 peptide 11‒19, 4-1BBL, and IL-12. Similar to our findings in mouse models, RTX-321 activated HPV 16 E7–specific CD8+ T cells in vitro, leading to their proliferation, expansion and enhanced effector function.

These preclinical findings support the potential of RTX-321 as an effective antigen-specific therapy for HPV 16-positive cancers. RTX-321 is currently being studied in a Phase 1 clinical trial for the treatment of patients with HPV 16-positive cancers.

From left to right authors Mengyao Luo, Andrea Schmidt, and Xuqing Zhang, preparing mouse surrogate cells for RTX-321 preclinical evaluation.


  1. Sahoo, K. et al. Molecular and biocompatibility characterization of red blood cell membrane targeted and cell-penetrating-peptide-modified polymeric nanoparticles. Mol. Pharm. 14, 2224–2235 (2017).
  2. Zhang, X. et al. Engineered red blood cells as an off-the-shelf allogenic anti-tumor therapeutic. Nat. Commun. 12, 2637 (2021).

Xuqing Zhang

Principal Scientist, Rubius Therapeutics