Figure 1.

Immune escape variants of cells in the tumor indicate an effective T cell response. HPV infection leads to unregulated cell proliferation and accumulation of chromosomal aberration. Cumulative genetic alterations in tumor cell subclones lead to the emergence of tumor cell variants with divergent characteristics, for example, loss of HLA expression. Selection pressure is exerted by the microenvironment of the tumor and immune response mechanisms. Over time, susceptible cells will be eliminated and resistant cells will regrow, to form a tumor consisting of predominantly immunoresistant cells and compromising immunotherapeutic strategies.