Phase Ib trial of folate binding protein (FBP)-derived peptide vaccines, E39 and an attenuated version, E39': An analysis of safety and immune response

Abstract

In this randomized phase Ib trial, we tested combining the E39 peptide vaccine with a vaccine created from E39', an attenuated version of E39. Patients with breast or ovarian cancer, who were disease-free after standard of care therapy, were enrolled and randomized to one of three arms. Arm EE received six E39 inoculations; arm EE' received three E39 inoculations followed by three E39'; and arm E'E received three E39' inoculations, followed by three E39. Within each arm, the first five patients received 500 μg of peptide and the remainder received 1000 μg. Patients were followed for toxicity, and immune responses were measured. This initial analysis after completion of the primary vaccination series has confirmed the safety of both vaccines. Immune analyses suggest incorporating the attenuated version of the peptide improves immune responses and that sequencing of E39 followed by E39' might produce the optimal immune response.

Trial registration: NCT02019524.

Keywords: Activation induced cell death; Attenuated vaccine; Breast cancer; Folate binding protein; Ovarian cancer; Peptide vaccine.

Figure 1

Vaccination Schedule. Patients received 6 inoculations (V1–V6), one every 3–4 weeks. Immunologic assay and DTH measurement was performed prior to the start of the primary vaccine series, then 1 and 6 months after the last inoculation (R0, RC1, RC6).

Figure 2

Consort Diagram through the Primary Vaccine Series. A total of 39 patients were enrolled, 30 of which completed the primary vaccine series (PVS). There were 10 patients in each arm. One low dose patient in the EE′ arm did not finish the PVS and was replaced by a high dose patient so a total of 14 patients received the low dose (5 EE, 4 EE′, 5 E′E) and 16 received the high dose (5 EE, 6 EE′, 5 E′E).

Figure 3

Toxicity Percentage of patients in each group experiencing maximum toxicities of each grade. There were no grade 3 or higher toxicities experienced by any patient. There were no significant differences in maximum toxicities between groups based on dosing or vaccine sequence.

Figure 4

Local reaction after first (V1), third (V3) and sixth (V6) inoculations. Figure 4A: All patients. The local reaction to the last inoculation of the PVS was significantly greater than the first (V6: 104.3±10.7mm vs V1: 48.4±11.4mm, p=0.001). Figure 4B: By dosing group. Both high dose and low dose groups showed significant increase at V6 vs V1 (low dose: 87.8±15.8 vs. 32.9±14.8mm, p=0.02; high dose: 127.3±9.2mm vs. 62.0±16.2mm, p=0.008). The high dose group showed consistently larger local reactions than the low dose group, with the difference being significant at V3 (V1: p=0.2, V3: p=0.02; V6: p=0.07). Figure 4C: By study arm. All groups showed an increase at V6 vs V1, but only the EE′ group showed a statistically significant increase (EE: p=0.07, EE′: p=0.002, E′E: p=0.14). *=p<0.05.

Figure 5

DTH at baseline (R0), 1 month (RC1), and 6 months (RC6) post-PVS. Figure 5A: DTH in all patients. There was a significant increase in DTH over the course of the trial (p=0.04). Figure 5B: DTH by dosing group. The low dose group had a significant increase in their DTH response through the trial (p=0.03). Figure 5C: DTH by study arm. The EE′ arm had the greatest response, with a significant increase over time compared to the EE and E′E arms (<0.001). Figure 5D: DTH by study arm AND dosing group. Within the EE′ arm, the low dose patients showed the largest increase in DTH, with a significant increase from R0 (0±0mm) to RC1 (48.5±14.5mm, p=0.01) and RC6 (58.8± 7.7mm, p<0.001). *=p<0.05.

Figure 6

CTL at baseline (R0), 1 month (RC1) and 6 months (RC6) post-PVS. Figure 6A: All patients CTL. There was no difference in levels of E39-specific CTLs (R:0.11±0.03%; RC1: 0.15±0.03%; RC6:0.13±0.02%, p=0.70). Figure 6B: CTL by dosing group. The high dose group had a non-significant increase in of E39-CTL between the R0 and RC1 (p=0.16), but a slight decrease at RC6. The low dose group had no significant change in CTL. Figure 6C: CTL by study arm. The EE′ (0.09±0.04% to 0.13±0.05%; p=0.57) and E′E (0.08±0.03% to 0.15±0.07%; p=0.32) groups experienced an increase in E39-specific CTL with the increase in the E′E group nearly a doubling in antigen-specific CTL.