In contrast to normal cells, tumor cells of multiple entities overexpress the Heat shock protein 70 (Hsp70) not only in the cytosol, but also present it on their plasma membrane in a tumor-specific manner. Furthermore, membrane Hsp70-positive tumor cells actively release Hsp70 in small extracellular vesicles with biophysical characteristics of exosomes. Due to conformational changes of Hsp70 in a lipid environment, most commercially available antibodies fail to detect membrane-bound and vesicular Hsp70. To fill this gap and to assess the role of vesicular Hsp70 in circulation as a potential tumor biomarker, we established the novel complete (comp)Hsp70 sandwich ELISA, using two monoclonal antibodies (mAbs), that is able to recognize both free and lipid-associated Hsp70 on the cell surface of viable tumor cells and on small extracellular vesicles. The epitopes of the mAbs cmHsp70.1 (aa 451–461) and cmHsp70.2 (aa 614–623) that are conserved among different species reside in the substrate-binding domain of Hsp70 with measured affinities of 0.42 nM and 0.44 nM, respectively. Validation of the compHsp70 ELISA revealed a high intra- and inter-assay precision, linearity in a concentration range of 1.56 to 25 ng/mL, high recovery rates of spiked liposomal Hsp70 (>84%), comparable values between human serum and plasma samples and no interference by food intake or age of the donors. Hsp70 concentrations in the circulation of patients with glioblastoma, squamous cell or adeno non-small cell lung carcinoma (NSCLC) at diagnosis were significantly higher than those of healthy donors. Hsp70 concentrations dropped concomitantly with a decrease in viable tumor mass upon irradiation of patients with approximately 20 Gy (range 18–22.5 Gy) and after completion of radiotherapy (60–70 Gy). In summary, the compHsp70 ELISA presented herein provides a sensitive and reliable tool for measuring free and vesicular Hsp70 in liquid biopsies of tumor patients, levels of which can be used as a tumor-specific biomarker, for risk assessment (i.e., differentiation of grade III vs. IV adeno NSCLC) and monitoring of therapeutic outcomes.

Purpose: Non-small cell lung cancer (NSCLC) is a fatal disease with poor prognosis. A membrane-bound form of Hsp70 (mHsp70) which is selectively expressed on high-risk tumors serves as a target for mHsp70-targeting natural killer (NK) cells. Patients with advanced mHsp70-positive NSCLC may therefore benefit from a therapeutic intervention involving mHsp70-targeting NK cells. The randomized phase II clinical trial (EudraCT2008-002130-30) explores tolerability and efficacy of ex vivo-activated NK cells in patients with NSCLC after radiochemotherapy (RCT). Patients and Methods: Patients with unresectable, mHsp70positive NSCLC (stage IIIa/b) received 4 cycles of autologous NK cells activated ex vivo with TKD/IL2 [interventional arm (INT)] after RCT (60-70 Gy, platinum-based chemotherapy) or RCT alone [control arm (CTRL)]. The primary objective was progression-free survival (PFS), and secondary objectives were the assessment of quality of life (QoL, QLQ-LC13), toxicity, and immunobiological responses. Results: The NK-cell therapy after RCT was well tolerated, and no differences in QoL parameters between the two study arms were detected. Estimated 1-year probabilities for PFS were 67% [95% confidence interval (CI), 19%-90%] for the INT arm and 33% (95% CI, 5%-68%) for the CTRL arm (P ¼ 0.36, 1-sided logrank test). Clinical responses in the INT group were associated with an increase in the prevalence of activated NK cells in their peripheral blood. Conclusions: Ex vivo TKD/IL2-activated, autologous NK cells are well tolerated and deliver positive clinical responses in patients with advanced NSCLC after RCT.

Background Breast cancer is the most common invasive tumor in women worldwide and the second cause of cancer-related deaths. After breast conserving surgery the tumor bed gets irradiated. Radiation-induced tumor cell death has been found to be associated with the release of damage-associated molecular patterns (DAMPs) including free Hsp70 that can stimulate inflammatory immune responses. Therefore, Hsp70 serum levels as well as the composition of lymphocyte subpopulations have been measured in breast cancer patients during therapy and in the follow-up period as potential predictors for clinical outcome. Methods The serum of 40 breast cancer patients, who received a breast-conserving surgery and adjuvant radiotherapy (RT) was examined for soluble, free Hsp70 using the R&D Human HSP70 DuoSet and lipHsp70 ELISA. Lymphocyte subpopulations and total lymphocyte counts were analysed by multiparameter flow cytometry in the peripheral blood. Blood samples were collected before (t1), after 30 Gy (t2) and 60 Gy (t3), 6 weeks (t4), 6 months (t5) and 1 year (t6) after RT. Clinical responses were assessed regularly up to 5 years after RT. Results Patients who developed a contralateral recurrence or metastases within the first 2 years after RT had significantly higher serum Hsp70 values at the end of RT (t3; p = 0.03) up to 6 weeks after RT (t4; p = 0.007) compared to patients who either remained disease-free or developed a secondary endometrial carcinoma. Clinicopathological parameters such as age, tumor size, grading and TNM-stage of the resected tumors, adjuvant chemotherapy and irradiation dose did not affect serum Hsp70 levels. Elevated free Hsp70 levels might be indicative for a chronic inflammatory response which could support tumor recurrence. Lymphocyte subpopulation analysis revealed lower NK cell counts after RT in recurrence/metastases patients as compared to disease-free patients. In contrast, no significant changes were observed in the proportion of T and B cells. Conclusion Longitudinal elevated serum levels of free Hsp70 up to 6 weeks after RT and dropping NK cell counts might be predictive for an unfavourable prognosis in patients with breast cancer.