The invention relates to pharmaceutical compositions comprising α-Gal BOEL for use in treating patients with tumors. The invention also relates to methods of treating tumors using said compositions. The invention discloses that following intratumoral injection of α-Gal BOEL, binding of the natural anti-Gal antibody to de novo expressed tumoral α-Gal epitopes induces inflammation resulting in an anti-Gal antibody mediated opsonization of tumor cells and their uptake by antigen presenting cells. These antigen presenting cells migrate to draining lymph nodes and activate tumor specific T cells thereby converting the treated tumor lesions into in situ autologous tumor vaccines. This therapy can be applied to patients with multiple lesions and in neo-adjuvant therapy to patients before tumor resection. In addition to the regression and/or destruction of the treated tumor, such a vaccine will help in the immune mediated destruction of micrometastases that are not detectable during the removal of the treated tumor. The invention further teaches the enhancement of anti-tumor α-Gal BOEL treatment by the use of antibodies that inhibit the activity of immunological checkpoints molecules.L'invention concerne des compositions pharmaceutiques comprenant de l'α-Gal BOEL pour son utilisation dans le traitement de patients présentant des tumeurs. L'invention concerne également des procédés de traitement de tumeurs utilisant lesdites compositions. Selon l'invention, à la suite d'une injection intratumorale d'α-Gal BOEL, la liaison de l'anticorps anti-Gal naturel à des épitopes d'α-Gal tumoraux exprimés de novo provoque une inflammation résultant en une opsonisation médiée par l'anticorps anti-Gal de cellules tumorales et leur absorption par des cellules présentatrices d'antigènes. Ces cellules présentatrices d'antigènes migrent vers les ganglions lymphatiques de drainage et activent les lymphocytes T spécifiques des tumeurs, convertissant ainsi les lésions tumorales traitées en vacci
