Lack of T-cell responses following autologous tumour lysate pulsed dendritic cell vaccination, in patients with relapsed osteosarcoma

BACKGROUND

Immunotherapy using autologous dendritic cell (DC) vaccination has not been systematically evaluated in osteosarcoma. We therefore conducted a phase I trial to assess feasibility, safety and tumour-specific immune responses in patients with relapsed disease.

PATIENTS AND METHODS

Of 13 recruited patients with relapsed osteosarcoma, 12 received 3 weekly vaccines of autologous DCs matured with autologous tumour lysate and keyhole limpet haemocyanin (KLH), to a maximum of 6 vaccinations. An additional 3 paediatric patients afflicted with other tumour types and with relapsed disease received vaccines generated with identical methodology. Immune responses were assessed using an ELISpot assay for the detection of interferon gamma, whilst interleukin-2 and granzyme B were additionally assessed in cases where interferon-γ responses were induced.

RESULTS

In total 61 vaccines, of homogeneous maturation phenotype and viability, were administered with no significant toxicity. Only in 2 out of 12 treated osteosarcoma cases was there an induction of specific T-cell immune response to the tumour, whilst a strong but non-specific immune response was induced in 1 further osteosarcoma patient. Immune response against KLH was induced in only 3 out of 12 osteosarcoma patients. In contrast, three additional non-osteosarcoma patients showed significant T-cell responses to vaccine.

CONCLUSION

We have shown the strategy of DC vaccination in relapsed osteosarcoma is safe and feasible. However, significant anti-tumour responses were induced in only 2 out of 12 vaccinated patients with no evidence of clinical benefit. Comparison of results with identically treated control patients suggests that osteosarcoma patients might be relatively insensitive to DC-based vaccine treatments.

Mycobacterium smegmatis phosphoinositols-glyceroarabinomannans. Structure and localization of alkali-labile and alkali-stable phosphoinositides

Lipoarabinomannans from fast growing Mycobacterium sp., namely AraLAMs, stimulate the early events of macrophage activation. The immunological activities of all of these AraLAMs drastically decrease with the loss of the mild alkali groups, which were believed to be restricted to the fatty acid residues from the phosphatidyl-myo-inositol anchor. This report reveals the presence and the structure of mild alkali-labile phosphoinositide units linked via the phosphate to the C-5 of the beta-D-Araf in the AraLAMs of Mycobacterium smegmatis, a fast growing mycobacterial species. Their structure was unambiguously established with a strategy based on both one-dimensional 31P and two-dimensional 1H-31P heteronuclear multiple quantum correlation spectroscopy (HMQC) and HMQC-homonuclear Hartmann-Hahn spectroscopy NMR experiments applied to native AraLAMs and to AraLAMs treated in mild alkali conditions. Next to these alkali-labile phosphoinositides estimated at three per molecule, two other mild alkali-stable phosphoinositide units were identified: the expected (myo-inositol-1)-phosphate-(3-glycerol) unit typifying the well known glycosylphosphatidylinositol anchor of the mannan core and, more surprisingly, one (myo-inositol-1)-phosphate-(5-beta-D-Araf) unit having the same structure as the alkali-labile ones. Moreover, these four phosphoinositide units were found capping the arabinan side chains. Thus, their different behavior toward mild alkaline hydrolysis was explained according to their accessibility to the alkali reagent. This novel class of LAMs, namely phosphoinositols-glyceroarabinomannans (PI-GAMs), are characterized by their phosphoinositide units but also by the absence of fatty acid residues. These PI-GAMs were found to elicit the secretion of tumor necrosis factor-alpha, suggesting that phosphoinositides are the major PI-GAM epitope involved in this process.