A phase Ib trial of pembrolizumab plus paclitaxel or flat-dose capecitabine in 1st/2nd line metastatic triple-negative breast cancer

Chemoimmunotherapy with anti-programmed cell death 1/ligand 1 and cytotoxic chemotherapy is a promising therapeutic modality for women with triple-negative breast cancer, but questions remain regarding optimal chemotherapy backbone and biomarkers for patient selection. We report final outcomes from a phase Ib trial evaluating pembrolizumab (200 mg IV every 3 weeks) with either weekly paclitaxel (80 mg/m² weekly) or flat-dose capecitabine (2000 mg orally twice daily for 7 days of every 14-day cycle) in the 1st/2nd line setting. The primary endpoint is safety (receipt of 2 cycles without grade III/IV toxicities requiring discontinuation or ≥21-day delays). The secondary endpoint is efficacy (week 12 objective response). Exploratory aims are to characterize immunologic effects of treatment over time, and to evaluate novel biomarkers. The trial demonstrates that both regimens meet the pre-specified safety endpoint (paclitaxel: 87%; capecitabine: 100%). Objective response rate is 29% for pembrolizumab/paclitaxel (n = 4/13, 95% CI: 10-61%) and 43% for pembrolizumab/capecitabine (n = 6/14, 95% CI: 18-71%). Partial responses are observed in two subjects with chemo-refractory metaplastic carcinoma (both in capecitabine arm). Both regimens are associated with significant peripheral leukocyte contraction over time. Response is associated with clinical PD-L1 score, non-receipt of prior chemotherapy, and the H&E stromal tumor-infiltrating lymphocyte score, but also by a novel 27 gene IO score and spatial biomarkers (lymphocyte spatial skewness). In conclusion, pembrolizumab with paclitaxel or capecitabine is safe and clinically active. Both regimens are lymphodepleting, highlighting the competing immunostimulatory versus lymphotoxic effects of cytotoxic chemotherapy. Further exploration of the IO score and spatial TIL biomarkers is warranted. The clinical trial registration is NCT02734290.

Paediatric adverse event rating scale: a measure of safety or efficacy? Novel analysis from the MADDY study

OBJECTIVE

The Pediatric Adverse Event Rating Scale (PAERS) measured adverse events of children aged 6-12 years with ADHD and emotional dysregulation in the Micronutrients for ADHD in Youth (MADDY) study, an eight week multi-site randomized clinical trial of a broad-spectrum multinutrient treatment. Treatment sensitivity of the PAERS was assessed by calculating the treatment difference in change of the item scores from baseline to end of the RCT.

METHODS

Principal component analysis retained 14 "adverse events" (out of 43 in the PAERS) that reflected ADHD symptoms and emotional dysregulation and was used to group the variables of interest. A combined score ranging from 0 to 5 was created based on symptom presence, functional impairment, and severity. Mean score change was calculated from baseline to week 8 by treatment (multinutrient vs placebo) with intention-to-treat and per-protocol samples. The study has been registered on clinicaltrials.gov as Micronutrients for ADHD in Youth (MADDY) Study, trial registration # NCT03252522 (https://clinicaltrials.gov/ct2/show/NCT03252522).

RESULTS

The 126 children in the ITT sample had a mean age of 9.8 (SD = 1.7), with majority (73%) male, and 72% diagnosed with ADHD prior to the study screening. Baseline presence of PAERS symptoms was similar between treatment groups: the highest proportion was ADHD symptoms, followed by Irritable symptoms. The micronutrient group showed a greater decrease (improvement) in the mean anxiety combined score than the placebo group with a between-group difference in change of -0.36 (95% CI: -0.67, -0.04; p = .03) with ITT data and -0.48 (95% CI: -0.81, -0.15; p = .005) with per-protocol (n = 93) data.

CONCLUSION

The multinutrient supplement did not result in more adverse events than placebo, suggesting it is a safe intervention. In addition to assessing actual adverse events, the PAERS may be a useful adjunct outcome measure for ADHD behaviors.

Changes in T-cell subsets and clonal repertoire during chemoimmunotherapy with pembrolizumab and paclitaxel or capecitabine for metastatic triple-negative breast cancer

BACKGROUND

Chemoimmunotherapy is a standard treatment for triple-negative breast cancer (TNBC), however, the impacts of different chemotherapies on T-cell populations, which could correlate with clinical activity, are not known. Quantifying T-cell populations with flow cytometry and T-cell receptor (TCR) immunosequencing may improve our understanding of how chemoimmunotherapy affects T-cell subsets, and to what extent clonal shifts occur during treatment. TCR immunosequencing of intratumoral T cells may facilitate the identification and monitoring of putatively tumor-reactive T-cell clones within the blood.

METHODS

Blood and tumor biopsies were collected from patients with metastatic TNBC enrolled in a phase Ib clinical trial of first or second-line pembrolizumab with paclitaxel or capecitabine. Using identical biospecimen processing protocols, blood samples from a cohort of patients treated for early-stage breast cancer were obtained for comparison. Treatment-related immunological changes in peripheral blood and intratumoral T cells were characterized using flow cytometry and TCR immunosequencing. Clonal proliferation rates of T cells were compared based on intratumoral enrichment.

RESULTS

When combined with pembrolizumab, paclitaxel and capecitabine resulted in similar time-dependent lymphodepletions across measured peripheral T-cell subsets. Their effects were more modest than that observed following curative-intent dose-dense anthracycline and cyclophosphamide (ddAC) (average fold-change in CD3⁺ cells, capecitabine: -0.42, paclitaxel: -0.56, ddAC: -1.21). No differences in T-cell clonality or richness were observed following capecitabine or paclitaxel-based treatments. Regression modeling identified differences in the emergence of novel T-cell clones that were not detected at baseline (odds compared with ddAC, capecitabine: 0.292, paclitaxel: 0.652). Pembrolizumab with paclitaxel or capecitabine expanded T-cell clones within tumors; however, these clones did not always expand within the blood. Proliferation rates within the blood were similar between clones that were enriched and those that were not enriched within tumors.

CONCLUSION

Chemoimmunotherapy for metastatic TNBC with pembrolizumab and capecitabine or paclitaxel resulted in similar peripheral T-cell subset lymphodepletion without altering T-cell clonal diversity. Regression modeling methods are applicable in immune monitoring studies, such as this to identify the odds of novel T-cell clones emerging during treatment, and proliferation rates of tumor-enriched T-cell clones.

94 Effects of chemoimmunotherapy on the peripheral blood: insights from immune monitoring of a phase Ib trial of pembrolizumab and paclitaxel or capecitabine for triple-negative breast cancer (TNBC)

Background

Pembrolizumab plus curative-intent dose-dense anthracycline-based chemotherapy (ddAC) is associated with improved outcome in PD-L1-negative TNBC,1 whereas in the metastatic setting, clinical benefit of chemoimmunotherapy (taxane or gemcitabine/carboplatin) is restricted to PD-L1-positive patients.2 We hypothesize that this discordance could be related to immunomodulatory differences of the various chemotherapies. On-treatment serial monitoring of peripheral blood and tumoral T cells can be used to compare the effects of various regimens. We also hypothesize that T cell clonal expansion may differ across the regimens, and that tumor-enriched T cell clones are more likely to be tumor-reactive and expand following chemoimmunotherapy.

Methods

Blood and tumor samples were collected from patients enrolled in a phase Ib clinical trial of palliative pembrolizumab and paclitaxel or capecitabine for metastatic TNBC, and from a contemporaneous cohort of patients treated with ddAC. T-cells were characterized using fresh whole blood flow cytometry and T-cell receptor (TCR) immunosequencing (immunoSEQ, Adaptive Biotechnologies) of DNA digests. Longitudinal regression was used to test the hypothesis that tumor-enriched T-cell clonotypes are more likely to expand in peripheral blood following therapy.

Results

When combined with pembrolizumab, paclitaxel versus capecitabine had similar effects on T-cells, resulting in a time-dependent lymphodepletion across all major T cell subsets (average CD3+ T cell fold-change capecitabine: -0.42, paclitaxel: -0.56, p = 0.80 t-test), whereas ddAC was associated with more profound lymphodepletion (CD3+ average fold-change: -1.21). Notably, ddAC was associated with higher odds of novel clonotype detection compared to capecitabine (odds ratio (OR): 3.42, 95% CI: 3.34–3.5) as well as compared to paclitaxel (OR: 1.53, 95% CI: 1.47–1.60). Significant expansion of tumoral clonotypes occurred in five patients receiving chemoimmunotherapy (average 4.2 unique clonotypes per patient, range 2–11). These clonotypes did not significantly expand over time in the blood. Similarly, T-cell clonotypes that were enriched within tumor did not exhibit measurable differences in serial trend within the peripheral blood.

Conclusions

Effects to T cell subsets and clonotypes are similar between capecitabine and paclitaxel when combined with pembrolizumab. ddAC was more profoundly lymphotoxic, but resulted in greater clonotype expansion. These findings offer mechanistic insight onto the differences in clinical activity observed with chemoimmunotherapy in early stage versus metastatic TNBC. We observed no strong association between tumor clonotype enrichment and peripheral clonotype expansion, highlighting the unmet need to develop methods of monitoring tumor-reactive T cell clones in the context of immunotherapy.

Acknowledgements

The authors would like to acknowledge collaborators at the Earle A. Chiles Research Institute and Adaptive Biotechnologies for mentorship and guidance. Support for the clinical trial (NCT02734290), which comprised the metastatic cohort was provided by Merck and the Providence Opportunity Fund. Laboratory services were provided at no cost by Adaptive Biotechnologies

Trial Registration

NCT02734290

References

Schmid P, Cortes J, Pusztai L, et al. Pembrolizumab for early triple-negative breast cancer. N Engl J Med 2020 Feb 27;382(9):810–821. doi: 10.1056/NEJMoa1910549.

Cortes J, Cescon DW, Rugo HS, et al. Pembrolizumab plus chemotherapy versus placebo plus chemotherapy for previously untreated locally recurrent inoperable or metastatic triple-negative breast cancer (KEYNOTE-355): a randomised, placebo-controlled, double-blind, phase 3 clinical trial. Lancet 2020;396(10265):1817–1828. doi:10.1016/S0140-6736(20)32531-9

Ethics Approval

All patients provided written, informed consent. The study protocols for the collection of specimens from the early-stage breast cancer cohort and from the metastatic TNBC clinical trial were separately approved by independent review boards at Providence Portland Medical Center and Cedars Sinai Medical Center (mTNBC clinical trial only).

Abstract PS17-07: Impact of chemotherapy (chemo) on t-cell maturation and clonal proliferation in early-stage and metastatic breast cancer

Background Adaptive immunity is initiated by T-cell receptor (TCR) engagement with cognate tumor antigen, leading to T-cell maturation (i.e. conversion from naïve to effector state), clonal proliferation, and potentially tumor elimination. Therefore, broad T-cell repertoire diversity could be an important determinant of anti-tumor immunity. In breast cancer, chemo may facilitate adaptive immunity, but conversely may also be lymphotoxic. We characterize the impacts of curative-intent chemo and palliative combination chemo/immune checkpoint inhibition (ICI) on lymphocyte quantity, maturation, and clonal proliferation. Methods Peripheral blood mononuclear cells (PBMCs) were collected at baseline and serially in stage I-III subjects receiving curative-intent chemo (dose-dense doxorubicin, cyclophosphamide, paclitaxel, n=20), and in stage IV subjects receiving palliative ICI (pembrolizumab) plus chemo (paclitaxel, n=15; or capecitabine, n=14). Flow cytometry was conducted on fresh PBMCs to minimize cellular losses related to cryopreservation. DNA was extracted for T-cell clonality analysis using the immunoSEQ Assay (Adaptive Biotechnologies) at deep resolution. T-cell richness, calculated using the iChao1 richness estimator was used to assess overall T-cell diversity. Results Both dose-dense chemo and palliative chemo/ICI were lymphodepleting, however dose-dense chemo was associated with greater reductions in CD4+ naïve T cell count (week 8 counts 34% vs. 96% of baseline, p<.001) and T-cell richness (week 8 richness 57% vs 90% of baseline, p<.001). These effects were durable, with reductions in lymphocyte subsets (ALC, CD4, CD8, naïve, effector, and central memory subsets) and T-cell richness (estimated rearrangements 4.37 vs 3.29 x 105/sample) sustained at metastatic relapse. T-cell richness correlated with CD4+ naïve cell proportion (R2=0.52), suggesting a major contribution of CD4+ naïve cells to overall T-cell diversity. In this dataset, acute memory T-cell expansions were observed following initiation of chemo, but only among younger patients (age<60). Conclusions Curative-intent cytotoxic chemotherapy durably alters the quantity and diversity of peripheral T-cells, particularly of naïve cells, contributing to lymphopenia and reduced T-cell richness at metastatic relapse. Acute expansions of EM subsets were also observed but only in younger individuals. These contrasting immunologic effects highlight the potential importance of sequencing of ICI relative to chemo, and raise concerns regarding age-related thymic involution and immunosenescence. Ongoing research is warranted to investigate the predictive/prognostic utility of T-cell diversity/quantity in breast cancer, and whether thymic T-cell regeneration can be targeted therapeutically to enhance immunotherapy response, for example with cytokine therapies (IL-12 or IL-7, NCT04095689) or sex steroid inhibition (NCT03650894).

Citation Format: Brie M Chun, Joanna Pucilowska, Valerie Conrad, Mark Schmidt, Isaac Kim, Paul Fields, Alison Conlin, Heather McArthur, David B Page. Impact of chemotherapy (chemo) on t-cell maturation and clonal proliferation in early-stage and metastatic breast cancer [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS17-07.

Evaluation of an in vitro endothelialized vascular graft under pulsatile shear stress with a novel radiolabeling procedure

OBJECTIVE

To improve the hemocompatibility of vascular grafts, endothelial cell (EC) seeding of biomaterials prior to implantation is critical. The current in vitro study was designed to investigate such a feasibility on a collagen-coated heparin-bonded graft and to evaluate cell detachment upon pulsatile shear stress.

MATERIALS AND METHODS

Endothelial cells (EA-hy-926) were seeded onto grafts. The endothelialization of the grafts was evaluated by the [3H]-thymidine incorporation, scanning electron microscopy (SEM) and histological examinations. After in situ EC radiolabeling with a novel 99mTc technique, the prostheses were exposed to pulsatile shear stress (0.27 N/m2), mimicking the shear rate occurring in a superficial femoral artery, for 3 h in a flow circuit and EC loss quantified by gamma camera detection.

RESULTS

Complete EC coverage was achieved after 5 days. Three hours of artificial perfusion resulted in a low EC loss (12.9+/-0.8%, n = 7). SEM shows EC withstanding shear stress in valleys of prosthesis circumvolutions.

CONCLUSIONS

These satisfactory results could be explained by the high affinity of EC for heparinized surfaces in addition to cell surface receptors involved in adhesion to collagen.

Expansion and differentiation of haemopoietic progenitor cells on endothelialized hydroxyapatite under static conditions

We have analysed the potential of an endothelialized hydroxyapatite matrix (HAP), a synthetic bone substitute, as a cellularized support for the expansion of haemopoietic progenitor cells. Scanning electron microscopy (SEM) showed that the endothelial cells (EC) tended to form a monolayer fitting closely to the matrix, and that the progenitors adhered to the EC layer. Endothelialized HAP supported the proliferation and differentiation of the progenitors with the addition of the exogenous cytokines IL-1, and IL-3. The expanded cell population essentially belonged to the myeloid and monocytic lineages, with a smaller percentage of the megakaryocyte lineage. In comparative experiments CD34+ progenitors were expanded on endothelialized tissue culture flasks, and a significant higher viability of the expanded cells was found with the endothelialized HAP. A high percentage (approx. 40%) of mature granulocytes was generated in accordance with the presence of differentiating cytokines such as G-CSF and GM-CSF at high concentrations in the coculture medium. Other cytokines that could be detected were IL-6, M-CSF, SCF, flt3-ligand. More than 50% of the expanded cell population was able to phagocytose bacteria and to generate an oxydative burst. These data indicate that cellularized HAP may be a useful matrix for stromal cell-based expansion systems.

Ex vivo expansion of haematopoietic progenitors on an endothelialized hydroxyapatite matrix

Autologous haematopoietic progenitor cell (HPC) transplantation is increasingly used to restore haematopoiesis after high-dose chemotherapy treatments. The present study was designed to analyse the ability of hydroxyapatite (HAP) seeded with endothelial cells (EC) to support the proliferation and differentiation of CD34+ HPC in static culture conditions. HAP is endothelializable as assessed by scanning electron microscopy and time-course DNA synthesis analysis using tritiated thymidine incorporated in EC isolated from human umbilical vein cord. Short-term coculture experiments in which CD34+ cells isolated from human cord blood were seeded on endothelialized HAP, were performed. Results show that endothelialized HAP is permissive to CD34+ cell expansion with a maximum expansion obtained between days 7 and 14 of coculture in the presence of IL-1 and IL-3 when compared with other experiments omitting either EC or interleukins. From morphological analyses, the expanded cell population mainly belonged to the myelocytic lineage with 33% mature cells (polymorphonuclear neutrophils and monocytes) at day 14 of coculture. The immature HPC could remain trapped within HAP while giving rise to a more mature progeny that exit from HAP microenvironment.

Ability of various inserts to promote endothelium cell culture for the establishment of coculture models

To select an insert suitable for human umbilical vein endothelial cell (HUVEC) culture, we compared several available inserts of 0.2 to 0.45 micron porosity: Cellagen (ICN), Transwell-COL (Costar), Millicell-HA and CM (Millipore), Anopore (Nunc), Cyclopore (Falcon) in comparison with a control surface (Thermanox). The requirements were: (i) to promote attachment, adhesion and proliferation of HUVEC (judged by [3H]thymidine incorporation into DNA at days 1, 3, 7); (ii) to allow HUVEC visualization by inverted, fluorescence microscopy for uptake of DiI-Ac-LDL and scanning electron microscopy, performed at day 9 after seeding. Because Transwell and Cellagen are collagen precoated and CM has to be coated for cell culture, we performed collagen coating (types I + III or IV) for non-pretreated inserts for the purpose of comparison. Our preferences comprise Transwell-COL, Cyclopore not coated or coated (whatever the collagen type), and Cellagen. However, on a quality/price ratio criterion, Cyclopore, even uncoated, is the insert of choice. The HA, CM and Anopore inserts, even coated, do not allow HUVEC growth but do not alter positive uptake of acetylated LDL.