Immunotherapy of experimental cancer by intralesional injection of emulsified nonliving mycobacteria: comparison of Mycobacterium bovis (BCG), Mycobacterium phlei, and Mycobacterium smegmatis

Nonpathogenic Mycobacterium brumae Inhibits Bladder Cancer Growth In Vitro, Ex Vivo, and In Vivo

BACKGROUND

Bacillus Calmette-Guérin (BCG) prevents tumour recurrence and progression in non-muscle-invasive bladder cancer (BC). However, common adverse events occur, including BCG infections.

OBJECTIVE

To find a mycobacterium with similar or superior antitumour activity to BCG but with greater safety.

DESIGN

In vitro, ex vivo, and in vivo comparisons of the antitumour efficacy of nonpathogenic mycobacteria and BCG.

INTERVENTION

The in vitro antitumour activity of a broad set of mycobacteria was studied in seven different BC cell lines. The most efficacious was selected and its ex vivo capacity to activate immune cells and its in vivo antitumour activity in an orthotopic murine model of BC were investigated.

OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS

Growth inhibition of BC cells was the primary outcome measurement. Parametric and nonparametric tests were use to analyse the in vitro results, and a Kaplan-Meier test was applied to measure survival in mycobacteria-treated tumour-bearing mice.

RESULTS AND LIMITATIONS

Mycobacterium brumae is superior to BCG in inhibiting low-grade BC cell growth, and has similar effects to BCG against high-grade cells. M. brumae triggers an indirect antitumour response by activating macrophages and the cytotoxic activity of peripheral blood cells against BC cells. Although no significant differences were observed between BCG and M. brumae treatments in mice, M. brumae treatment prolonged survival in comparison to BCG treatment in tumour-bearing mice. In contrast to BCG, M. brumae does not persist intracellularly or in tumour-bearing mice, so the risk of infection is lower.

CONCLUSIONS

Our preclinical data suggest that M. brumae represents a safe and efficacious candidate as a therapeutic agent for non-muscle-invasive BC.

PATIENT SUMMARY

We investigated the antitumour activity of nonpathogenic mycobacteria in in vitro and in vivo models of non-muscle-invasive bladder cancer. We found that Mycobacterium brumae effectively inhibits bladder cancer growth and helps the host immune system to eradicate cancer cells, and is a promising agent for antitumour immunotherapy.

Induction of T cell responses and recruitment of an inflammatory dendritic cell subset following tumor immunotherapy with Mycobacterium smegmatis

Mycobacteria and their cell wall components have been used with varying degrees of success to treat tumors, and Mycobacterium bovis BCG remains in use as a standard treatment for superficial bladder cancer. Mycobacterial immunotherapy is very effective in eliciting local immune responses against solid tumors when administered topically; however, its effectiveness in eliciting adaptive immune responses has been variable. Using a subcutaneous mouse thymoma model, we investigated whether immunotherapy with Mycobacterium smegmatis, a fast-growing mycobacterium of low pathogenicity, induces a systemic adaptive immune response. We found that M. smegmatis delivered adjacent to the tumor site elicited a systemic anti-tumor immune response that was primarily mediated by CD8(+) T cells. Of note, we identified a CD11c(+)CD40(int)CD11b(hi)Gr-1(+) inflammatory DC population in the tumor-draining lymph nodes that was found only in mice treated with M. smegmatis. Our data suggest that, rather than rescuing the function of the DC already present in the tumor and/or tumor-draining lymph node, M. smegmatis treatment may promote anti-tumor immune responses by inducing the involvement of a new population of inflammatory cells with intact function.

Closely related mycobacterial strains demonstrate contrasting levels of efficacy as antitumor vaccines and are processed for major histocompatibility complex class I presentation by multiple routes in dendritic cells

Mycobacteria expressing recombinant antigens are already being developed as vaccines against both infections and tumors. Little is known about how dendritic cells might process such antigens. Two different mycobacterial species, the fast-growing Mycobacterium smegmatis and the slow-growing M. bovis M. bovis BCG, were engineered to express a model tumor antigen, the K(b)-restricted dominant cytotoxic T-lymphocyte epitope OVA(257-264). Recombinant M. bovis BCG but not recombinant M. smegmatis conferred protection to mice challenged with the B16-OVA tumor cell line. We went on to investigate whether the contrast in antitumor efficacy could be due to differences in how dendritic cells process antigen from the two mycobacterial strains for class I presentation. Both strains of mycobacteria caused phenotypic maturation of dendritic cells, but recombinant M. smegmatis infection led to a greater degree of dendritic cell maturation than recombinant M. bovis BCG infection. Antigen from recombinant M. smegmatis was processed and presented as OVA(257-264) on K(b) molecules by the dendritic cell line DC2.4 but not by bone marrow-derived dendritic cells (BMDC) or splenic dendritic cells. In contrast, antigen from recombinant M. bovis BCG was presented by all three dendritic cell types as long as the mycobacteria were viable. Such presentation was dependent on proteasome function and nascent major histocompatibility complex (MHC) class I molecules in DC2.4 cells but independent of the proteasome and transporter associated with antigen processings (TAP) in BMDC and splenic dendritic cells. These data demonstrate for the first time that antigen vectored by the slow-growing M. bovis BCG but not that vectored by fast-growing, readily destroyed M. smegmatis is processed and presented on MHC class I by in vitro-generated dendritic cells, which has implications for recombinant microbial vaccine development.

Adjuvant immunotherapy with nonviable Mycobacterium smegmatis in resected primary lung carcinoma. A randomized clinical trial of 219 patients

Two hundred and nineteen patients with resected lung carcinoma were randomized 3 weeks after surgery between two treatment arms: a control group (110 cases) and an immunotherapy group (109 cases). The immunostimulant was a nonviable saprophytic mycobacterium, M. smegmatis, given monthly by subcutaneous injection in four sites. The two groups were equivalent in terms of prognostic factors, including a nonsignificant difference favoring the control group based on the N (node) classification. This interim analysis was carried out on June 1, 1981. Treatment comparison by the log-rank test did not show any significant differences between these two groups in regards to disease-free interval and overall survival. There was no significant difference between the two groups after stratification of the comparison according to the N classification or adjustment with a subset of eight prognostic parameters through the Cox model. The initially expected difference (20% 1-year survival) will probably not be achieved, given these interim results, but patients will continue to be treated and followed-up according to the protocol as to allow further evaluation of this nonspecific immunotherapy.

Stimulation of non-specific anti-tumour resistance in the mouse using cell wall preparations from four BCG substrains

The comparative anti-tumour activity of cell walls, deproteinized cell walls and cell wall skeleton (CWS) isolated from four BCG substrains (Canadian, Russian, Glaxo and Swedish) was determined against Ehrlich ascitic carcinoma in CF-1 mice and against L1210 lymphoid leukaemia in B6D2F1/J mice. In Ehrlich carcinoma, the protocol of injection was shown to be of critical importance, since high and low levels of protection and even facilitation of tumour growth were observed according to the protocol used. The oil emulsion used as the vehicle for injection of the fractions (control groups) induced facilitation of tumour growth with some protocols. The highest levels of protection were observed when treatment was performed on day -6 for a single i. p. injection or on days -14 and 0 for two injections. Using the former protocol of immunization, the highest level of protection was detected with cell walls and deproteinized cell walls. CWS isolated from the Canadian and Glaxo substrains were found to be inactive, whereas those isolated from the Swedish and Russian substrains induced significant levels of protection. In L1210 leukaemia, very few preparations induced significant protection. CWS preparations did not induce protection. Canadian and Russian deproteinized cell walls and Canadian cell walls (100 and 250 micrograms, respectively) induced some protection. The use of different protocols of injection did not increase the anti-tumour activity of the Canadian cell walls. The most active preparation in both tumour systems was that of Canadian deproteinized cell walls.

A specific vaccine effective against stage I and stage II malignant disease in guinea pigs. Effect of variations in preparations and storage

Guinea pigs, each with an established, syngeneic dermal line 10 tumor and lymph node metastases, were immunized by intradermal injection of a mixture of irradiated line 10 cells and an emulsion containing heat-killed BCG. Immunization eradicated 7- or 10-day-old dermal tumors (about 10 or 12 mm in diameter, respectively) and prevented growth of microscopic lymph node metastases. Fourteen-day-old dermal tumors (about 15 mm in diameter) were not rejected by immunization. Guinea pigs with stage II disease (21-day-old dermal tumors and palpable metastases in the first draining lymph node) were treated by excision of the dermal tumor and the first draining lymph node, and by specific immunization. This treatment eliminated tumor cells remaining in the second draining lymph nodes. The surgical treatment alone was not curative, palpable metastases in the second draining lymph nodes progressed and the animals died (some with visible lung metastases). Emulsions containing killed BCG were good adjuvants even after prolonged storage at 4 degrees C, but lost most of their adjuvant activity after autoclaving or freezing.