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377 IL-15 treatment enhances the in vivo anti-tumor efficacy of sipuleucel-T by activating CD8+ T and NKT effector cells, augmenting tumor infiltration, and reversing immunoresistance pathways
  1. Russell Pachynski1,
  2. Muhammad A Saeed1,
  3. Bo Peng1,
  4. Kevin Kim1,
  5. Ariel Borkowski1,
  6. Brian Van Tine1,
  7. Nadeem Sheikh2,
  8. Tuyen Vu2,
  9. Daniel Thorek1 and
  10. Todd Fehniger1
  1. 1Washington University School of Medicine, St Louis, MO, USA
  2. 2Dendreon Pharmaceuticals, Seattle, WA, USA
  • Journal for ImmunoTherapy of Cancer (JITC) preprint. The copyright holder for this preprint are the authors/funders, who have granted JITC permission to display the preprint. All rights reserved. No reuse allowed without permission.


Background Metastatic castration-resistant prostate cancer (mCRPC) represents the most lethal form of prostate cancer. Sipuleucel-T (sip-T) is an autologous therapeutic produced using a tumor antigen-cytokine fusion protein, and the only FDA approved cellular immunotherapy for mCRPC patients. Sip-T significantly improves overall survival (OS), but has limited impact on PSA and radiographic responses. Here, we present the first high dimensional analysis of sip-T in detail using a mass cytometric approach, and highlight immune subsets and inhibitory/stimulatory receptors expression. Furthermore, we show the effects of IL-15 on the anti-tumor efficacy of sip-T using in vitro and in vivo and studies.

Methods We performed a comprehensive assessment of the sip-T product (n=13 samples) collected from prostate cancer patients using mass cytometry (CyTOF). Control and IL-15 stimulated sip-T were evaluated, and changes in leukocyte subsets as well as markers of activation and exhaustion were identified. Finally, we examined the effects of IL-15 on cytotoxicity of sip-T against human prostate cancer lines using in vitro cytotoxicity assays and in vivo studies in NSG mice. (figure 1)

Results CyTOF analysis revealed that CD3+ T cells constituted the highest proportion of sip-T, followed by B-cells, natural killer (NK) cells, NKT, and monocytes, with only a small percentage of dendritic cells. Following sip-T stimulation with IL-15, a significant expansion and activation of CD8+ T-cell and NK cell populations was seen. Co-culture of sip-T with IL-15 and control or prostate-relevant antigens showed significant activation and expansion of CD8 T and NKT cells in an antigen-specific manner. Furthermore, IL-15 stimulated sip-T showed significantly higher in vitro tumor cytotoxicity compared to control or other cytokines tested. Adoptive transfer of IL-15 treated sip-T into NSG mice resulted in potent prostate tumor growth inhibition compared to control. Evaluation of tumor-infiltrating lymphocytes revealed a 2 to 14-fold higher influx of sip-T and a significant increase in interferon (IFN)-γ producing CD8+ T and NKT cells within the tumor microenvironment in the IL-15 group. Tumor transcriptomic analyses revealed IL-15 treatment was able to reverse immunoresistance induced by sip-T alone.

Conclusions This is the first comprehensive study to evaluate sip-T from prostate cancer patients using high dimensional CyTOF analysis, and reveals potential targets for improvement of sip-T efficacy. Furthermore, this is the first pre-clinical in vivo prostate tumor model of sip-T adoptive transfer, showing that IL-15 treatment can significantly enhance anti-tumor efficacy, effector immune cell activation and tumor infiltration, and reverse mediators of immune suppression.

Ethics Approval Sip-T samples from patients were collected after their verbal and written consent under an Washington University IRB approved banking protocol (#201411135). All animal studies were performed in accordance with approved Washington University (St. Louis, MO) and NIH Institutional Animal Care and Use Committee guidelines under an approved protocol (No. 20–0383).

This is an open access article distributed in accordance with the Creative Commons Attribution Non Commercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited, appropriate credit is given, any changes made indicated, and the use is non-commercial. See

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