Table of Con­tents | Arti­cle doi: 10.17742/IMAGE.BR.11.1.9 | PDF

Imaging Human Breast Tumours in Different Species: How Human Are They?

Gabrielle M. Siegers, Julia Schuel­er, Hon Sing Leong, Lynne-Marie Postovit
Abstract; In a gedanken­ex­per­i­ment, we pose the philo­soph­i­cal ques­tion as to whether human breast can­cer cells or tis­sues can still be con­sid­ered human after trans­plan­ta­tion into anoth­er species. Along­side med­ical research images illus­trat­ing xeno­trans­plan­ta­tion, we pro­vide descrip­tions of how tis­sues were pre­pared for imag­ing. In addi­tion, we dis­cuss how such mod­els enable fur­ther under­stand­ing of can­cer and pro­vide invalu­able tools for test­ing new therapies.
Resume : Dans un gedanken­ex­per­mi­nent nous posons la ques­tion philosophique de savoir si les tis­sus et cel­lules de can­cer du sein humain peu­vent tou­jours être con­sid­érés comme humains après qu’ils ont été trans­plan­tés dans une autre espèce. En plus de pho­togra­phies de recherche médi­cale illus­trant la xéno­trans­plan­ta­tion, nous offrons des descrip­tions expli­quant com­ment des tis­sus ont été pré­parés pour la visu­al­i­sa­tion. Nous débat­tons en out­re de la manière dont de tels mod­èles per­me­t­tent une meilleure com­préhen­sion du can­cer et offrent des out­ils ines­timables pour tester de nou­velles thérapeutiques.

Cancer researchers use mod­el sys­tems in order to under­stand mech­a­nisms of can­cer ini­ti­a­tion and pro­gres­sion, and also to test new treat­ments. This is done before such treat­ments are test­ed in peo­ple, and is gov­erned by the Helsin­ki Dec­la­ra­tion (World Med­ical Asso­ci­a­tion) as well as nation­al ani­mal care com­mit­tee guide­lines (such as those of the CCAC in Cana­da, OLAW in the USA, and GV-Solas in Ger­many), which ensure eth­i­cal prac­tices are employed in the use of both human tis­sues and ani­mals in research.

Xenograft (xenos, Greek = for­eign) mod­els involve trans­plant­i­ng human cells or tis­sue into mice that have lit­tle to no immune sys­tems (which would reject the trans­plants). For diag­nos­tic pur­pos­es, pieces of breast tumours removed dur­ing surg­eries are pre­served and sent to his­tol­ogy labs for pro­cess­ing. Tumours are embed­ded in paraf­fin and sliced very thin­ly, after which these “sec­tions” are stained with hema­toxylin and eosin (H&E) dyes. These allow pathol­o­gists to see the sizes and shapes of cells under the micro­scope, to dis­tin­guish cell nuclei from oth­er struc­tures with­in the cell and also to iden­ti­fy struc­tures out­side of cells, termed extra­cel­lu­lar matrix. An exam­ple of an H&E stained sec­tion of a human tumour is shown in pan­el A. The cor­re­spond­ing H&E sec­tion from the mod­el sys­tem derived from this very tumour—the patient derived xenograft (PDX, Charles River)—is depict­ed in pan­el B. The sim­i­lar­i­ties are strik­ing, and there­in lies the pow­er of the PDX. The human tumour piece has been implant­ed into a mouse, allowed to grow in size, and then pieces there­of are fur­ther implant­ed into more mice. Through­out this process, these tumour pieces retain most char­ac­ter­is­tics of the orig­i­nal malig­nan­cy; this enables cre­ation of a tis­sue bank that can be used for test­ing promis­ing anti-can­cer drugs and immunotherapies.

The ques­tion aris­es, how­ev­er, as to whether human breast can­cer cells or breast tumour tis­sues can still be con­sid­ered human after they have been trans­plant­ed into anoth­er species, such as a mouse or chick­en embryo. To sur­vive in anoth­er species, a human tumour must con­nect with the blood sys­tem of that species, which allows var­i­ous sup­port cells to enter the tumour and help it thrive. So how human is the tumour at this point?

One defin­ing fea­ture of human cells is their expres­sion of spe­cif­ic pro­teins called human leuko­cyte anti­gens (HLA) on their sur­face (World Health Orga­ni­za­tion, Park and Terasa­ki). Using a tech­nique called immuno­his­to­chem­istry, we can detect the pres­ence or absence of HLA on cells in tumour sec­tions. HLA expres­sion on the tumour in pan­el B is shown in pan­el C: brown stain­ing indi­cates the pres­ence of human HLA and the lack of stain indi­cates mouse cells. Thus, the breast tumour, that looks so sim­i­lar to its all-human coun­ter­part in A, has now become a hybrid of human and mouse.

Anoth­er type of xenograft mod­el used in breast can­cer research is the chick­en chorioal­lan­to­ic mem­brane (CAM) mod­el (Nowak-Sli­win­ka et al.). Egg shells are removed from chick­en embryos so that we can visu­al­ize them eas­i­ly using a micro­scope. Human can­cer cell lines are often engi­neered in the lab to pro­duce a flu­o­res­cent pro­tein, so that they can be eas­i­ly dis­tin­guished from the host (mouse or chick­en, in this case) and mon­i­tored using dif­fer­ent types of imag­ing tech­niques. These are then inject­ed into the CAM and are used to learn about many aspects of can­cer pro­gres­sion. Pan­el D shows human breast can­cer cells that express green flu­o­res­cent pro­tein (GFP) that have formed a tumour in a CAM; here, the cir­cu­la­tion sys­tem of the chick­en embryo has been dyed red (rho­damine bound to lectin on the cell sur­face). Again, the chick­en cells and sys­tem sup­port human tumour growth, allow­ing us to study aspects of breast can­cer and how metas­ta­sis occurs (Leong et al.).

How human are these breast tumours? It is a ques­tion worth con­sid­er­ing. For now, we can at least say that they are human enough for us to learn more about human breast can­cer, and test new treat­ments that will hope­ful­ly lead to bet­ter out­comes for breast can­cer patients.

Works Cited

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Leong, H.S. et al. “Assess­ing can­cer cell migra­tion and metasta­t­ic growth in vivo in the chick embryo using flu­o­res­cence intrav­i­tal imag­ing.” Meth­ods in Mol­e­c­u­lar Biol­o­gy, vol. 872, 2012, pp. 1-14, doi: 10.1007/978-1-61779-797-2_1.

Nowak-Sli­win­s­ka, P. et al. “The chick­en chorioal­lan­to­ic mem­brane mod­el in biol­o­gy, med­i­cine and bio­engi­neer­ing.” Angio­gen­e­sis, vol. 17, no. 4, 2014, pp. 779-804, doi: 10.1007/s10456-014-9440-7.

Park, I. and P. Terasa­ki. “Ori­gins of the first HLA speci­fici­ties.” Hum Immunol­o­gy, vol. 61, no. 3, 2000, pp. 185-89, doi: 10.1016/s0198-8859(99)00154-8.

World Health Orga­ni­za­tion. “Nomen­cla­ture for fac­tors of the HL-a sys­tem.” Bul­letin of the World Health Orga­ni­za­tion, vol. 39, no. 3, 1969, pp. 483-86.

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