Researchers hope the phenomenon can lead to a new path in treating cancer in humans.
By Thomas H. Maugh II, L. A. Times Staff Writer
May 9, 2006
White blood cells from mice that are naturally immune to cancer cured tumors in other mice and provided them with lifelong immunity to the disease, researchers reported Monday.

The finding indicates the existence of a biological pathway previously unsuspected in any species. A small team of researchers is working to understand the genetic and immunological basis of the surprising phenomenon.

Preliminary studies hint at the existence of a similar resistance in humans. Researchers hope that harnessing the biological process could lead to a new approach to treating cancer.

Sources: LA Times: Injected Cells Cure Tumors in Mice [may require registration, free]

Proc. Natl. Acad. Sci. USA, 10.1073/pnas.0602382103
Transferable anticancer innate immunity in spontaneous regression/complete resistance mice
Zhen Cui, et al. OPEN ACCESS ARTICLE

Abstract - Download full text .pdf. free.

Spontaneous regression/complete resistance (SR/CR) mice resist very high doses of cancer cells that are lethal to WT mice even at low doses. In this study, we show that this resistance is mediated by rapid infiltration of leukocytes, mostly of innate immunity, in both primary and repeated challenges. Formation of rosettes with infiltrating natural killer cells, neutrophils, and macrophages was required for the subsequent destruction of cancer cells through rapid cytolysis. Highly purified natural killer cells, macrophages, and neutrophils from the SR/CR mice independently killed cancer cells in vitro. The independent killing activity by each subset of effector cells is consistent with the observation that the resistance was abolished by depleting total infiltrating leukocytes but not by depleting only one or two subsets of leukocytes. The resistance was completely transferable to WT recipient mice through SR/CR splenocytes, bone marrow cells, or enriched peritoneal macrophages, either for prevention against subsequent cancer challenges or eradication of established malignancy at distant sites.

Excerpt from the Discussion section (page 5 in .pdf) in the original PNAS article:

The resistance to cancer cells in SRCR mice involves the ability
of host leukocytes to detect unique signals from cancer cells, to
migrate to the cancer site, and to establish tight physical contact,
resulting in the rupture of the cancer cells. SRCR leukocytes
apparently rely on a predetermined mechanism for recognizing
some signal common to all cancer cell lines tested so far. The
concept that the resistance against cancers is mediated by innate
immunity is supported by several facts. First, the genetically
determined anticancer response required no prior exposure.

Second, innate immune cells remained the major responding
effector cells during repeated challenges. Third, leukocytes from
naıve SRCR mice displayed killing activity in vitro before any
in vivo exposure to cancer cells. Fourth, transfer of highly
purified M conferred a similar resistance in WT recipients. In
contrast, involvement of transplant rejection for the anticancer
response is highly unlikely, because it usually takes at least 2
weeks after the primary exposure to the target.
However, there has been an obvious enhancement of resistance
in terms of speed and tumor burden during repeated
responses. Despite a lack of evidence that the components of
adaptive immunity contributed to the resistance, we still could
not completely rule out a possible role for adaptive immunity in
the enhancement of anticancer responses…….

The second major finding of this study was that resistance
could be entirely transferred to cancer-sensitive mice for both
treatment and prevention of malignancy. Even highly aggressive
forms of malignancy with large tumor burdens could be completely
eradicated systemically. This efficacy in mice suggests
that the anticancer strategy in SRCR mice may point to a future
therapeutic direction in which adverse side effects of treatment
are minimal. The transferred resistance functioned in both
immune-competent (Fig. 12, which is published as supporting
information on the PNAS web site) and immune-deficient
recipients. Our findings from AT also suggest that effective
resistance to transplanted cancer cells in SRCR mice is mediated
entirely by transferable cellular components of the immune
system. The successful long-term retention of resistance was
achieved in the absence of adaptive immunity of either donor or
recipient…….

Another observation in this study was that large established
solid s.c. tumors in WT mice completely regressed after transfer
of SRCR leukocytes. This finding is remarkable given that
reversal of this kind of malignancy has, to our knowledge, never
before been reported. This regression took place with or without
the presence of stroma. Together, these findings suggest that the
resistance has implications in both prevention and treatment of
cancers in mice. These findings suggest that the resistance
mechanism may recognize a common property when malignancies
are presented, locally or distantly, in different forms or
different cell types.