Bcma Heteroclitic Peptide Encapsulated Nanoparticle Enhances Antigen Stimulatory Capacity and Tumor-Specific CD8⁺ cytotoxic T Lymphocytes Against Multiple Myeloma

Background:

B-cell Maturation Antigen (BCMA), a member of the tumor necrosis factor (TNF) receptor superfamily and the receptor for binding of B cell activating factor (BAFF) and a proliferation-inducing ligand (APRIL), is a promising therapeutic target for MM. Due to its restricted expression pattern on MM cells and plasma cells along with its role in promoting MM cells growth, survival, and drug resistance, BCMA is being targeted by several immunotherapeutic strategies including antibodies, immunotoxins, bispecific T-cell engagers, and CAR-T cells. Recently, we have identified nanomedicine-based therapeutics targeting BCMA as a promising area of translational research to effectively evoke and augment anti-tumor responses in MM patients. Several nanomedicines are available and more advanced nanoparticle constructs are under development for antigen encapsulation. To this end, we have designed a heteroclitic BCMA peptide encapsulated nanoparticle-based cancer vaccine to overcome the limitations of free peptide vaccines including poor peptide stability, susceptibility to enzyme degradation, and low antigen uptake and delivery. Furthermore, the nanotechnology-based cancer vaccine was developed to induce more robust BCMA-specific CD8⁺ cytotoxic T lymphocytes (CTL) activities in MM patients, with more sustained antigen release and increased bioavailability and presentation of the immunogenic peptide. Here, we examine the potential of a novel nanomedicine-based therapeutic delivery system specific to BCMA antigen to treat the patients with MM.

Objective:

The purpose of this study was to design the optimal nanoparticle encapsulated BCMA antigen constructs to efficiently evoke and develop the BCMA-specific CD8⁺ CTL with functional anti-myeloma activities.

Findings:

Nanoparticles [liposome or poly(D,L-lactide-co-glycolide) (PLGA)] with different antigen-release kinetics demonstrated their capacity to effectively deliver heteroclitic BCMA peptideto antigen-presenting cells and evoke BCMA antigen-specific CTL with anti-MM activities. The heteroclitic BCMA peptide encapsulated nanoparticles demonstrated a higher uptake by human dendritic cells than free peptide, with the highest uptake mediated with liposome-based nanoparticles. In contrast, BCMA-specific CTL induced with PLGA-based nanoparticle demonstrated the highest functional activities and specific immune responses against MM cells. The PLGA/BCMA peptide nanoparticle induced BCMA-specific CTL displayed the highest increases in CD107a degranulation, the antigen-specific CD8⁺ T cells proliferation and Th-1 type cytokines (IFN-g, IL-2, TNF-a) production to MM patients' tumor cells and MM cell lines compared to BCMA-CTL generated with free BCMA peptide or liposome/BCMA peptide nanoparticle. These observations were aligned with the highest level of CD28 costimulatory molecules upregulation, Tetramer⁺ CTL generation and peptide-specific responses within the BCMA-CTL generated by PLGA/BCMA nanoparticles. Furthermore, the PLGA/BCMA nanoparticles triggered a more robust induction of antigen-specific memory CD8⁺ T cells, which demonstrated significantly higher anti-tumor activities, evidenced by CD107a degranulation and IFN-g production, compared to non-memory CD8⁺ T cells within the BCMA-CTL. Especially, the increased central memory CTL development and their anti-tumor activities evoked by PLGA/BCMA peptide were associated with the optimal peptide release kinetics and enhanced immunogenicity of the antigen via this nanotechnology. Thus, these results demonstrate that the heteroclitic BCMA peptide encapsulated nanoparticle strategy supports the peptide delivery into dendritic cells and then subsequently to T cells, resulting in effective induction of BCMA-specific central memory CTL with poly-functional activities against MM.

Significance:

These results demonstrate the utility of nanotechnology using encapsulated heteroclitic BCMA peptide to enhance the immunogenicity of BCMA peptide-specific therapeutics against MM. Importantly, our observations provide the framework for therapeutic application of PLGA-based heteroclitic BCMA peptide delivery to enhance the BCMA-specific memory T cell immune responses, overcome the limitations of current peptide-based cancer vaccine, and improve the patient outcome in MM.