Analysis of Circulating Immune Biomarkers by Race in Men with Metastatic Castration-Resistant Prostate Cancer Treated with Sipuleucel-T

Among racial subgroups, Black men have the highest prostate cancer–specific death rate, yet they also exhibit prolonged overall survival compared with White men when treated with standard therapies, including sipuleucel-T. Differential immune responses may play a role in these observations. We compared circulating immune markers from 54 men (18 Black and 36 White) with metastatic castrate-resistant prostate cancer who received sipuleucel-T and were enrolled on an immune monitoring registry. Markers included longitudinal serum cytokine concentrations, humoral responses, and cellular immunity from baseline until 52 weeks after sipuleucel-T administration. Black men had statistically significantly higher median concentrations of T_H2-type (interleukin [IL]-4, IL-10, and IL-13) and inflammatory cytokines (IL-2, IL-12, and IL-6) compared with prostate-specific antigen-matched White men both at baseline and 52 weeks after sipuleucel-T (2-sided P < .05). No differences by race were seen in either the antigen-specific T-cell response or the humoral responses to the immunizing antigen PA2024 and select secondary antigens.

Long-term Sculpting of the B-cell Repertoire following Cancer Immunotherapy in Patients Treated with Sipuleucel-T

Sipuleucel-T is an autologous cellular immunotherapy, administered as three infusions, for metastatic castration-resistant prostate cancer (mCRPC). Sipuleucel-T induces T- and B-cell responses to prostatic acid phosphatase (PAP), correlating to improved survival. The long-term impact of sipuleucel-T on tumor antigen-specific immunologic memory remains unknown, in particular, B-cell responses, as measured by antigen-specific antibody responses and B-cell receptor (BCR) sequences. To evaluate whether sipuleucel-T could induce long-term immunologic memory, we examined circulating B-cell responses before and after sipuleucel-T treatment in two groups of patients with mCRPC: those who had previously received sipuleucel-T (treated; median, 8.9 years since the previous treatment) versus those who had not (naïve). Before re-treatment, previously treated patients exhibited persistent antibody responses as well as more focused and convergent BCR repertoires with distinct V(D)J gene usage compared with naïve patients. After re-treatment, previously treated patients maintained high-frequency clones and developed more convergent BCRs at earlier time points unlike naïve patients. With the first sipuleucel-T infusion specifically, previously treated patients had less shuffling within the 100 most abundant baseline clones. In contrast, naïve patients exhibited great BCR turnover with a continued influx of new B-cell clones. Social network analysis showed that previously treated patients had more highly organized B-cell repertoires, consistent with greater clonal maturation. Higher treatment-induced BCR clonality correlated with longer survival for naïve patients. These results demonstrated the capacity of sipuleucel-T to induce long-term immune memory and lasting changes to the B-cell repertoire.

The association of humoral antigen spread (AgS) with cytotoxic T lymphocyte (CTL) activity after sipuleucel-T (sip-T) treatment in two phase II clinical studies: STAMP and STRIDE

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Background: Sip-T is an FDA-approved immunotherapy for metastatic castration-resistant prostate cancer. Sip-T generates CTL and humoral antigen activity, as measured by CD107a expression on PAP or PA2024 specific CD8+ T cells. These specific CTL activities were correlated with improved overall survival in several studies STAMP (NCT01487863) and STRIDE (NCT01981122) [1]. We examined whether CTL activity enables humoral response generation, hypothesizing that killing a target cell with immunotherapy releases antigens that generate a secondary antibody response, extending the effect. Methods: Using samples from patients who received sip-T in these studies, correlation between CTL activity and AgS responses to primary (PA2024, PAP) and secondary (PSA, LGALS3, LGALS8, KRAS, ERAS, KLK2) antibodies over time was assessed. Using R statistics software, a Wilcoxon signed rank test assessed differences across time (Wk, week: WK0, week 0, etc) and Spearman rank test for correlation between CTL activity and AgS responses. Results: In STAMP, PAP-specific CTL activity at WK0 was positively correlated with LGALS3 antibody responses at WK6, WK10, WK14 and WK26; likewise, PAP-specific CTL activity at WK6 was positively correlated with antibody response to PAP at WK0 (P = 0.035). In STRIDE, PAP-specific CTL activities at WK0 and both PAP- and PA2024-specific CTL activities at WK6 were positively correlated with LGALS8 antibody response at WK52. Plus, PAP- and PA2024- specific CTL activities at WK6 had significant, positive correlation with PA2024 antibody responses at WK0. In both, PA2024-specific CTL activity at WK26 was positively correlated with number of secondary antigen responses at WK10 and WK14. Conclusions: In all, PA2024-specific CTL activity at WK6 was positively correlated with antibody response to primary antigens (PA2024 and PAP) and 4 secondary antigens – PSA, KRAS, ERAS and KLK2 at multiple time points. In summary, treatment with sip-T in mCRPC appears to invoke the tumor immunity cycle, wherein tumor cell death releases compounds that act as secondary epitopes resulting in antigen spread. [1] DOI: 10.1158/1078-0432.CCR-18-0638. Clinical trial information: NCT01487863.

Antigen (Ag) spread after sipuleucel-T and correlation with overall survival (OS): A real-world experience

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Background: Sipuleucel-T is an autologous cellular immunotherapy for asymptomatic or minimally symptomatic metastatic castration-resistant prostate cancer. In IMPACT (NCT00065442), a phase 3 trial, sipuleucel-T-induced immune responses against target Ag prostatic acid phosphatase (PAP) or PA2024, a recombinant protein consisting of PAP and granulocyte macrophage colony stimulating factor, correlated with OS (Sheikh 2013). Additionally, sipuleucel-T-induced immunoglobulin G (IgG) responses against secondary, non-target Ag (i.e. Ag spread) and the breadth of Ag spread also correlated with improved OS (GuhaThakurta 2015). Here we assessed Ag spread and OS in real-world patients from PRIME (NCT01727154), an immune monitoring sub-study of sipuleucel-T trials Methods: IgG levels in pre and wk 6 (2 wk post sipuleucel-T completion) sera from PRIME (n = 100) were quantified using Luminex xMAP. IgG responses to secondary Ag (LGALS3, PSA, KLK2, LGALS8, K-Ras, E-Ras) were defined as ≥ 1.5-fold increase over baseline. OS associations with individual Ag responses and total number of Ag per patient were assessed using the Kaplan-Meier method. Hazard ratios (HR) were estimated using a Cox Proportional Hazard Model. Results: IgG responses to ≥1 secondary Ag were observed in ≥72% of patients. Individual IgG responses to LGALS3, K-Ras, and LGALS8 at wk 6 were significantly associated with OS. Furthermore, breadth of Ag spread positively correlated with OS (Table); as the total number of Ag responses per patient increased, OS improved compared to patients with no secondary IgG responses. Conclusions: The results presented are consistent with findings from the prior phase 3 trial IMPACT. Secondary Ag responses were generated in real-world patients treated with sipuleucel-T, and these responses correlated with OS. Furthermore, breadth of Ag spread also correlated with improved OS. Clinical trial information: NCT01727154. [Table: see text]

Tracking of long-term B-cell memory responses using B-cell receptor (BCR) sequencing in prostate cancer (PC) patients (pts) treated with sipuleucel-T (sip-T)

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Background: Sip-T is an autologous cellular immunotherapy for asymptomatic or minimally symptomatic metastatic castration-resistant prostate cancer (mCRPC). Sip-T’s induction of B-cell responses to PAP and other antigens correlates with improved survival (Sheikh 2013, GuhaThakurta 2015). Cancer vaccine-induced changes to BCR repertoire are unknown. To assess changes in BCR repertoire upon booster treatment, we compared patients retreated with sip-T (P10-1) to treatment-naïve patients (STRIDE). Methods: STRIDE pts (N = 52) received sip-T with concurrent or sequential enzalutamide for mCRPC (Petrylak 2015). P10-1 pts (N = 8) previously treated with sip-T for androgen-dependent PC were retreated with a booster course for mCRPC, after a median of 8.9 years (Beer 2017). Blood samples were collected at baseline (wk 0) and during (wk 2, 4)/post-sip-T (wk 6, 26, 52). Deep sequencing was performed using the ImmunoSEQ assay (Adaptive Biotechnologies). BCR diversity was assessed by clonality, and BCR dynamics by fold-change analysis (Zhang 2017). Results: BCR repertoire had significantly higher clonality in P10-1 vs STRIDE (wk 0: p = 0.003, wk 2: p < 0.001, wk 4: p < 0.001), suggestive of a more focused BCR repertoire. P10-1 also showed increased clonality from wk 0 to 4 (p = 0.063), whereas STRIDE showed a significant increase in clonality from wk 0 to 6 (p = 0.039), suggesting that BCR repertoire focused earlier in P10-1. Starting at wk 2, more clones remained in the repertoire in P10-1, indicating that sip-T stimulated immunologic memory early, after 1st retreatment (p < 0.05). There was less change over time (clonal shuffling) within the 100 most abundant baseline clones in P10-1 (p = 0.080), suggesting more relevant clones preexisted at baseline and enriched over time. After the first two sip-T infusions, more clones contracted in P10-1 (p = 0.027, p = 0.014), whereas more new clones were generated in STRIDE (p = 0.083, p = 0.003). Conclusions: Sip-T induces long-lasting changes in the BCR repertoire. Sip-T retreatment leads to quicker focusing of BCR repertoire than initial treatment. These results are consistent with sip-T inducing durable immunologic memory.

Clonotypic T-cell responses in metastatic castration-resistant prostate cancer (mCRPC) patients (pts) treated with standard sipuleucel-T (sip-T) compared with patients receiving a booster treatment

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Background: Sip-T is an FDA-approved autologous cellular immunotherapy for asymptomatic or minimally symptomatic mCRPC. Neoadjuvant sip-T induced activated T-cell infiltration to the prostate tissue (Fong 2014) and broadened the T cell receptor (TCR) repertoire vs control (Sheikh 2016). To test if sip-T induces memory T-cell responses, we compared treatment-induced changes in TCR repertoire of treatment-naïve pts (STRIDE) with those retreated with sip-T (P10-1). Methods: In STRIDE (N=52), pts received sip-T with concurrent or sequential enzalutamide (Petrylak 2015). In P10-1 (N=8), pts previously treated with sip-T in an androgen-dependent setting were retreated with a booster course after a median of 8.6 years (Beer 2013). PBMCs were collected at baseline and during/post–sip-T. Deep sequencing was performed using the ImmunoSEQ assay (Adaptive Biotechnologies). TCR diversity was assessed by Shannon diversity index and clonality. TCR dynamics was evaluated by Morisita’s distance (Zhang 2017). Results: Baseline TCR diversity was similar between the two trials (p=0.590, Shannon diversity index; p=0.700, clonality). Significant decreases in clonality were observed from baseline to wk 4 (p<0.001) and wk 6 (p=0.030) in STRIDE, but not in P10-1, indicating more expansion of T cell clones in STRIDE. Morisita’s distance was significantly higher at wk 2 (p=0.040) and 26 (p=0.013) in STRIDE vs P10-1, indicating a more consistent TCR repertoire in STRIDE across timepoints. The proportion of the clones enriched after sip-T treatment was significantly higher in P10-1 vs STRIDE (wk 6: p=0.007, wk 26: p=0.015, wk 52: p=0.026). The extent of change within the top 100 most abundant TCR sequences (clonal shuffling) was greater and initiated earlier in P10-1 vs STRIDE. Conclusions: Initial sip-T treatment of naïve mCRPC pts programs the TCR repertoire, which is maintained over time. Consistent with immunologic memory, retreatment with sip-T rapidly expands the number of enriched T-cell clones persisting up to 1 year after retreatment, which is characteristic of immunological boosting following successful treatment.

Blood-based predictive biomarkers for overall survival (OS) in patients (pts) receiving the immunotherapy sipuleucel-T (sip-T)

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Background: Sip-T is an FDA-approved immunotherapy for the treatment of asymptomatic or minimally symptomatic metastatic castration-resistant prostate cancer (mCRPC). While baseline prostate-specific antigen level correlates with prolonged OS in pts treated with sip-T, biomarkers predictive of OS remain elusive. Gene expression signatures in peripheral blood (PB) correlate with prognosis in mCRPC (Ross et al, Lancet Oncol. 2012). This study sought to identify a candidate PB gene signature predictive of OS benefit with sip-T. Methods: PB mononuclear cells from sip-T or control (CN) mCRPC pts in the IMPACT trial (NCT00065442) were collected prior to leukapheresis. Affymetrix gene chip (HGU133P2) screening evaluated gene expression; association of gene expression with OS was performed using a multivariate Cox proportional hazards regression model, where OS was fit to gene expression and the 2003 baseline Halabi prognostic variables. The top 50 gene candidates were selected for qPCR confirmation. Results: Out of the 50 gene candidates selected for qPCR confirmation, 5 genes were associated with OS. High expression of SNTB1 and CHI3L2 and low expression of SYNGR3, AURKC, and ZNF268 were associated with improved OS in sip-T–treated pts but not in CN arm pts. A composite gene score (CGS) was calculated incorporating expression of these genes. In a CGS tertile analysis, OS in the top and middle sip-T tertiles was significantly better compared with the corresponding CN groups (Table). The lowest sip-T tertile had a median OS similar to that of the CN arm. Conclusions: CGS based on baseline gene expression may predict OS outcomes for mCRPC pts receiving sip-T. Compared with the CN arm, OS was significantly improved in the top two tertiles of sip-T–treated pts; OS in the bottom tertile was similar to the CN arm. Clinical trial information: NCT00065442. [Table: see text]

Antigen spread (AgS) after sipuleucel-T (sip-T): A cross-trial comparison of 4 sip-T clinical trials of patients (pts) with prostate cancer (PC)

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Background: Sip-T, an FDA-approved autologous immunotherapy for pts with asymptomatic or minimally symptomatic metastatic castration-resistant PC (mCRPC), is manufactured from peripheral blood mononuclear cells cultured with PA2024, a fusion antigen of prostatic acid phosphatase (PAP) conjugated to granulocyte macrophage colony-stimulating factor. In sip-T–treated pts, antibody responses to PA2024/PAP (target antigens) and AgS (antibody responses to secondary [2°] antigens) correlate with improved OS (Sheikh 2013; GuhaThakurta 2015). We assessed if a greater magnitude of AgS would be observed in an earlier PC disease stage when the immune system is more intact. Methods: Pt serum was from 1 non-metastatic, androgen-dependent PC (ADPC) sip-T trial (STAND, sip-T + androgen deprivation, NCT01431391) and 3 mCRPC sip-T trials (IMPACT, sip-T vs control, NCT00065442; STAMP, sip-T + abiraterone acetate, NCT01487863; STRIDE, sip-T + enzalutamide, NCT01981122). Using a Luminex assay, mean fold-change in IgG responses to target and 2° cancer-related antigens (PSA, LGALS3, LGALS8, ERAS, KRAS, KLK2) was evaluated from baseline to wk 6. Results: AgS was evaluated in 308 pts. The mean fold-change in IgG responses to target antigens was greater for ADPC vs mCRPC pts (p < 0.01). Moreover, the magnitude of IgG responses was greater for most 2° antigens in ADPC vs mCRPC pts (p < 0.05; Table), except for PSA and KLK2 in ADPC vs STRIDE pts. Conclusions: The magnitude ofantibody responses to target and 2° antigens was greater earlier in the PC disease course, consistent with increased antigen-presenting cell activation in ADPC vs mCRPC pts. Increased AgS likely reflects stronger sip-T–induced immune responses, previously associated with extended OS in mCRPC (Sheikh 2013; GuhaThakurta 2015). Future research is warranted on the clinical benefit of sip-T earlier in the PC disease course and the potential impact of androgen suppression on the magnitude of AgS and outcomes. Clinical trial information: NCT01431391; NCT00065442; NCT01487863; NCT01981122. [Table: see text]

Humoral Immune Response against Nontargeted Tumor Antigens after Treatment with Sipuleucel-T and Its Association with Improved Clinical Outcome

PURPOSE

Antitumor activity of cancer immunotherapies may elicit immune responses to nontargeted (secondary) tumor antigens, or antigen spread. We evaluated humoral antigen spread after treatment with sipuleucel-T, an immunotherapy for asymptomatic or minimally symptomatic metastatic castration-resistant prostate cancer (mCRPC), designed to target prostatic acid phosphatase (PAP; primary antigen).

EXPERIMENTAL DESIGN

Serum samples from patients with mCRPC enrolled in the placebo-controlled phase III IMPACT study (evaluable n = 142) were used to assess humoral antigen spread after treatment with sipuleucel-T. Immunoglobulin G (IgG) responses to self-antigens (including tumor antigens) were surveyed using protein microarrays and confirmed using Luminex xMAP. IgG responses were subsequently validated in ProACT (n = 33), an independent phase II study of sipuleucel-T. Association of IgG responses with overall survival (OS) was assessed using multivariate Cox models adjusted for baseline prostate-specific antigen (PSA) and lactate dehydrogenase levels.

RESULTS

In patients from IMPACT and ProACT, levels of IgG against multiple secondary antigens, including PSA, KLK2/hK2, K-Ras, E-Ras, LGALS8/PCTA-1/galectin-8, and LGALS3/galectin-3, were elevated after treatment with sipuleucel-T (P < 0.01), but not control. IgG responses (≥ 2-fold elevation posttreatment) occurred in ≥ 25% of patients, appeared by 2 weeks after sipuleucel-T treatment, and persisted for up to 6 months. IgG responses to PSA and LGALS3 were associated with improved OS in sipuleucel-T-treated patients from IMPACT (P ≤ 0.05).

CONCLUSIONS

Sipuleucel-T induced humoral antigen spread in patients with mCRPC. IgG responses were associated with improved OS in IMPACT. The methods and results reported may identify pharmacodynamic biomarkers of clinical outcome after sipuleucel-T treatment, and help in clinical assessments of other cancer immunotherapies. See related commentary by Hellstrom and Hellstrom, p. 3581.