Xenotransplantation: Still a hope?

Emanuele CozziUniversity Hospital - Padua

An approach to the problem of Xenograft rejection

Donor

Recipient

Production of “engineered” animals

• Immunology

• Physiology

• Biosafety

• Ethics and regulations

Xenotransplantation: Key issues

• Immunology

• Physiology

• Biosafety

• Ethics and regulations

Xenotransplantation: Key issuesand genetic engineering

• Immunology

• Physiology

• Biosafety

• Ethics and regulations

Clinical Xenotransplantation: Key issues

• Pharmacological immunosuppression

• Tolerance inducing regimens

• Genetic engineering of the pig

To deal with immunological issues 3 approaches have been followed

A clinical trial should be considered when:

• ~ 60% survival has been achieved of a life-life-supporting organsupporting organ in a NH primate for at least 3 months

• Some animals should achieve a longer survival ( 6 months)

• In the absence of life-threatening complications from IS

Recommendations of the ISHLT Xenotransplantation Advisory Committee

[Cooper et al:JHLT 2000, 19:1125]

• Anti CD154 has been used as part of the immunosuppression in the study with the longest survivor (median 63 days; range: 16-179d) .

• Perhaps antiCD40 may lead to similar results?

• All grafts underwent AHXR which was characterized by the presence of thrombotic micoangiopathy (little cellular infiltrate; no obvious interstitial hemorrhage)

Pharmacological immunosuppression

[Kuwaki et al, Nat Med 2005; Shimizu et al A J Pathol 2008]

In contrast, a clinical applicable regimen was used in the study with the longest median survival (median 96 days; range: 15-137d) of heterotopic hearts:

Pharmacological immunosuppression

[Anti CD20 + ATG] + Tacro+ Rapa + steroids+TPC + SPXSPX

• No consumptive coagulopathy• treatable infections• Rejection in 2 cases only!

[McGregor et al, J Thorac Cardiovasc Surgery 2005]

• 179 days for a heterotopic heart xenograft

• 56 days for an orthotopic heart xenograft

• 90 days for a life supporting kidney xenograft

• >180 days in at least series of islet xenografts

Longest survival of primates transplanted with porcine organs or cells

• Hering et al [nature Med. 2006]

• Cardona et al [Nature Med. 2006]

• Larsen et [ATC, San Francisco 2007]

• Gianello et al [IXA-IPITA-CTS, Minneapolis 2007]

Six-month survival in islet pig-to-primate xenotransplantation

• Hering et al [nature Med. 2006]• Cardona et al [Nature Med. 2006]

Anti-CD25+ anti-CD154 + FTY + RAD+ LFMAnti CD25 + anti CD154 + sirolimus + Belatacept

• Larsen et [ATC, San Francisco 2007]Anti CD25 + anti CD40 + sirolimus + Belatacept

• Gianello et al [IXA-IPITA-CTS, Minneapolis 2007]Encapsulation with alginate, no immunosuppression

Six month survival in islet pig-to-primate xenotransplantation

• Hering et al [nature Med. 2006]• Cardona et al [Nature Med. 2006]

Anti-CD25+ anti-CD154 + FTY + RAD+ LFMAnti CD25 + anti CD154 + sirolimus + Belatacept

• Larsen et [ATC, San Francisco 2007]Anti CD25 + anti CD40 + sirolimus + Belatacept

• Gianello et al [IXA-IPITA-CTS, Minneapolis 2007]Encapsulation with alginate, no immunosuppression

Six month survival in islet pig-to-primate xenotransplantation

In all cases, W

ILD TYPE

islets were

used

Longest survival of porcine islet xenografts (II)

Dufrane et al, Minneapolis 2007

PrimatePrimatePrimatePrimate

0 4 8 12 14 20 24

Weeks

-40

200

400

600

Longest survival of porcine islet xenografts

Hering et al, Nature Medicine 2006

[BSM]+FTY720+RAD+ABI793+LFM

• Pharmacological immunosuppression

• Tolerance inducing regimens

• Genetic engineering of the pig

To deal with immunological issues 3 approaches have been followed

• Co-transplantation of vascularised thymic tissue with GalT-KO kidneys using a tolerance inducing regimen

• prolonged survival of functioning kidney xenografts, without the development of anti-donor T cell responses or of induced antibody (median: 69; range 31-83 days)

Tolerance inducing regimens

[Yamada et, Nat Med 2005]

• Pharmacological immunosuppression

• Tolerance inducing regimens

• Genetic engineering of the pig

To deal with immunological issues 3 approaches have been followed

Improving graft survival and genetic engineering of the pig

Better comprehension of the rejection mechanisms

Identification of new targets for specific intervention

Genetic engineering of the pig genome

• Complement regulation (CD55, CD46, CD59)

• Immunogenicity (αGALT-KO)

• Coagulation (CD39, TM, TFPI, TF-KO, TM...)

• Immunomodulation (CTLA4Ig, HLA-G)

• Ischemia/IRI (CD39, A20, VEGF...)

Genetic engineering of the pig : Possible targets of intervention

[adapted from D’Apice et al, Xenotransplantation 2008]

Substantial improvements in the technology:

• Identification of novel targets of intervention

• Cloning of the pig

• Multigene constructs (adaptation of FMV 2A syst.)

• Very recent identification of pig embryonic stem (ES) cells

Genetic engineering

[D’Apice et al, Xenotransplantation 2008]

• Immunology

• Physiology

• Biosafety

• Ethics and regulations

Clinical Xenotransplantation: Key issues

• Molecular incompatibilities have been demonstrated between pig and man (coagulation, liver)

• A consumptive coagulopathy is invariably observedinvariably observed following xenotransplantation. However, we now know that DICDIC is NOT the rule in primate xenotransplantation (neither in baboons, nor in cynos)

• In all cases, to date no insormountable physiological or anatomical incompatibilities have been reported (life-supporting renal/cardiac models)

Pig-to-primate physiological compatibility

• Immunology

• Physiology

• Biosafety

• Ethics and regulations

Clinical Xenotransplantation: Key issues

• difficult to eliminate

• maintained in a latent or intracellular state in an asymptomatic host

• Porcine endogenous retrovirus (PERV)• Herpesviruses• Circovirus etc.

• as yet unidentified

Potential microbial problems in xenotransplantation

Potentially problematic microbes are those:

• Genetically engineering of the donor

• siRNA

• (PERV- knock out pigs)

• In a retrospective study in 160 patients exposed to living porcine tissues, no signs of PERV-related infection (current, past or latent) or disease were observed.

• A line of minipigs carrying PERV that do not replicate in vitro in human cells has been reported

• PERV replication inhibited by antiviral agents (including AZT)

• (Anti-PERV vaccine prior to exposure to porcine tissues)

PERVs: important aspects

• Pig breeding and close monitoring in SPF facilities

• The search for potential unknown pathogens remains a central issue.

• latest advances in biomolecular technology are proving to be very useful in the timely identification of unknown microorganism potentially present in human tissues.

• These include: PCR Differential display screening Microarray

• Application of molecular engineering to safety aspects

Xenotransplantation and Zoonoses

A New Arenavirus in a Cluster of Fatal Transplant-Associated Diseases [Gustavo Palacios et al. N Engl J Med 2008;Volume 358:991-998]

Unknown viruses in allotransplantation

Organ donor

liver

kidney

kidney

• Immunology

• Physiology

• Biosafety

• Ethics and regulations

Clinical Xenotransplantation: Key issues

Position paper of the Ethics Committee of the International Xenotransplantation Association (2003)

• Respect for the person and informed consent

• The problem of “xenotourism”

• Securing benefit over harm through pre-clinical studies

• Ethics and the use of animals

• Clinical trials if appropriate regulatory oversight by national body and IRB

• Favourable risk/benefit assessment (for the patient and for society)

Regulatory aspects: key documents

• U.S. Public Health Service (PHS) Guideline on Infectious Disease Issues in Xenotransplantation [January 19, 2001]

• Guidance for Industry - Source Animal, Product, Preclinical and Clinical Issues Concerning the Use of xenotransplantation Products in Humans – FDA April 2003

• Recommendation Rec(2003)10 of the Committee of Ministers to EU member states on xenotransplantation

• Canada (2001)• Australia (2003)• New Zealand regulatory framework for xenotransplantation

• WHO

Regulatory aspects: the role of WHOWHO Assembly adopted in May 2004 the Health Assembly Resolution WHA57.18 that:

• Urges Member States to "allow xenotransplantation only when effective national regulatory control and surveillance mechanisms overseen by National Health Authorities are in place“

• Requires the Director-General of the WHO to support Member States in the development and regulation of xenotransplantation.

• Refers to the concept of “harmonisation” [“cooperation” of the EU rec (2003)10]

Global Consultation on Regulatory Requirements for Xenotransplantation, held in Changsha (China)

Are we currently performing clinical xenotransplantation trials?

Clinical xenotransplantation activities

• We are aware of 2 biotech companies “interacting” at the FDA level (University of Minneapolis and UPMC)

• Conditional approval of a xenotransplantation trial by the New Zealand Goverment (LCT)

• An ongoing clinical trial in Russia (LCT)

Conclusions• Considerable progress has been achieved in the field of

solid organ and cell xenotransplantation.

• We have a better understanding of the rejection process and refined our genetic engineering techniques.

• This has lead to novel immunosuppressive strategies and the generation of new lines of engineered animals

• Islet xenografts certainly work longterm and solid xenograft may soon work just as well.

• However, current EFFICACY DATA do not justify progression to the clinic.

• For the time beeing we have to design, under the guidance of the WHO, a globally applicable ethical and regulatory framework, to allow safe initiation of xenotransplantation trials.