Coculturing diverse clonal populations prevents the early-stage neoplastic progression that occurs in the separate clones

Abstract

Most human cancers are of monoclonal origin and display many genetic alterations. In an effort to determine whether clonal expansion itself could account for the large number of genetic alterations, we compared spontaneous transformation in cloned and uncloned populations of NIH 3T3 cells. We have reported that progressive transformation of these cells, which is driven by the stress of prolonged contact inhibition at confluence, occurs far more frequently in cultures of recent monoclonal origin than in their uncloned progenitors. In the present work we asked how coculturing six clones at early and late stages of progression would affect the dynamics of transformation in repeated rounds of confluence. When coculture started with clones in early stages of transformation, marked by light focus formation, there was a strong inhibition of the progression to the dense focus formation that occurred in separate cultures of the individual clones. In contrast, when coculture started after the individual clones had progressed to dense focus formation, there was selection of transformants from the clone producing the largest and densest foci. Mixing the cells of a single clone with a large excess of uncloned cells from a subline that was refractory to transformation markedly decreased the size of dense foci from clones in transit from light to dense focus formation, but had much less effect on foci from clones with an established capacity for dense focus formation. The major finding of protection against progression by coculturing clones in early stages of transformation suggests that the expansion of a rogue clone in vivo increasingly isolates many of its cells from genetically stabilizing interactions with surrounding clones. Such clonal isolation might account for the increase in mutation rates associated with the dysplasia in colorectal adenomas that signifies the transition between benign and malignant growth.progressive transformation ͉ clonal susceptibility ͉ polyclonal resistance ͉ critical mass ͉ age-dependence of cancer I t generally is accepted that most human cancers are clonal in origin (1-3). Extremely large numbers of genetic changes have been found in these growths. For example, more than 25% of the heterozygous loci in sporadic cases of colorectal cancer exhibit loss of heterozygosity (LOH) (4). More than half of the cases of esophageal adenocarcinoma reveal extensive LOH of polymorphic microsatellite markers along the entire length of a single chromosome (5). A large increase in the frequency of mutations is found in the highly dysplastic lesions that mark the transition in colorectal adenomas to carcinomas (6). This finding suggests that the lesions have to reach a certain minimal size and degree of disorganization to drive the many genetic changes that underlie progression to malignancy. It had been proposed earlier that a critical mass of cells bearing the same or similar mutations was needed to produce the malignant state (7). Quantitation of the critical mass concept closely fit the age-related increa...

Neutropenia dynamics in a case of T‐LGL lymphoproliferation illustrate rapid turnover of granulocyte progenitors

“…Lymphocytosis remained moderate over time (range 1460–6464/mm 3 ), possibly reflecting stabilization that regulates polyclonal proliferation. Recent studies have shown that mixing clonal populations strongly inhibits early‐stage neoplastic progression observed for isolated clones (17). This may also reflect a putative intrinsic protective mechanism activating spontaneous apoptosis when the tumour clone expands, as shown in recurrent cycling of a case of lymphoma (18).…”