Ex Parte Evans et al

Board of Patent Appeals and Interferences

Feb 27, 2003

08464271 (B.P.A.I. Feb. 27, 2003)

The opinion in support of the decision being entered today was not written
for publication and is not binding precedent of the Board.

Paper No. 56

UNITED STATES PATENT AND TRADEMARK OFFICE
__________

BEFORE THE BOARD OF PATENT APPEALS
AND INTERFERENCES
__________

Ex parte RONALD M. EVANS,
EMILIANA F. BORRELLI, and
RICHARD A. HEYMAN
__________

Appeal No. 2001-1293
Application No. 08/464,271
__________

ON BRIEF
__________

Before SCHEINER, ADAMS, and GRIMES, Administrative Patent Judges.

GRIMES, Administrative Patent Judge.

DECISION ON APPEAL

This is a decision on appeal under 35 U.S.C. § 134 from the examiner’s
final rejection of claims 3-8, 12, 29, 31-41, 44, and 45, all of the claims remaining.
Claims 44 and 38-40 are representative and read as follows:
44. A method for selectively inhibiting growth or causing death of
a tissue-type or cell line in an intact organism;

wherein said tissue-type or cell line comprises endogenous
thymidine kinase and further comprises DNA encoding and
expressing an exogenous enzyme that selectively converts a latent
toxin into a cell toxin in said tissue-type or said specific cell line,
where said DNA is operatively linked to a promoter specific for said
tissue-type or said cell line,
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said method comprising administering to said organism an
amount of said latent toxin effective to trigger generation of said cell
toxin by enzymatic conversion of the latent toxin; thereby
selectively inhibiting growth or causing death of at least a
substantial portion of said tissue-type or cell line.

38. A method according to Claim 42 wherein said exogenous enzyme
is selected from non-mammalian enzymes that catalyze the
conversion of the latent toxin into a cell toxin for said cell line.

40. A method according to Claim 39 wherein said viral enzyme is
herpes simplex thymidine kinase.

The examiner relies on the following references:
Ledley, “Somatic gene therapy for human disease: Background and prospects.
Part I,” The Journal of Pediatrics, Vol. 110, pp. 1-8 (1987)

Kappel et al. (Kappel), ”Regulating gene expression in transgenic animals,”
Current Opinion in Biotechnology, Vol. 3, pp. 548-553 (1992)

Mullen, “Metabolic suicide genes in gene therapy,” Pharmac. Ther., Vol. 63, pp.
199-207 (1994)

Claims 3-8, 12, 29, 31-41, 44, and 45 stand rejected under 35 U.S.C.
§ 112, first paragraph, as nonenabled.
We affirm in part.
Background
The specification discloses a method of “establishing stable transgenic cell
populations and then selectively ablating (i.e., negatively selecting for) specific
cell types and/or cell lineages in such transgenic cell populations at desired
stages of development or differentiation.” Page 1.
According to the invention method, (C) cells that express
exogenous gene (G) and thus contain enzyme (E) within the
transgenic cell population, when exposed to a specific latent toxin,
i.e., non-toxic drug substance that enzyme (E) converts into a
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substance that is toxic to the cells (C), are eliminated from the
original cell population. In this manner, the toxic potential of the cell
(C) is actualized, thus allowing specific cell (C) types within the
transgenic cell population to be negatively selected for, i.e., to be
ablated. In addition, by controlling the amount of expression of
gene (G) in cell (C), which can be done, for example, by linking the
gene (G) to a “weak” or a “strong” tissue-specific promoter, and by
controlling the rate, dose and/or timing of the exposure of cell (C) to
the non-toxic drug compounds, it is possible to control the degree
and timing of the resulting genetic ablation.

Id., page 10.
The specification discloses several exemplary tissue-specific promoters
suitable for use in the disclosed method. See page 8. The specification also
discloses that the exogenous enzyme can be herpes simplex virus thymidine
kinase (HSV-TK). See, e.g., pages 16-17. No other examples of suitable
exogenous genes or enzymes are disclosed, although the specification notes
that “[o]ther enzymes which can be used in the practice of the present invention
are non-mammalian, i.e., enzymes which are not native to the host cells
contemplated for the generation of a transgenic cell population.” Page 15.
The specification discloses that the method “makes it possible to progress
from mild cellular degeneration to almost complete destruction of a specific cell
line, thus providing the ability to (1) create valuable animal models with which to
study lineage formation and cell function; (2) treat diseased individuals by
selective ablation of disease cells, and (3) selectively ablate any cell line.”
Specification, page 19.
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Discussion
The claims stand or fall together. Appeal Brief, page 6. We will consider
independent claim 44 as representative of the claimed method. The remaining
claims will stand or fall with claim 44.1
Claim 44 is directed to a method for killing cells of a particular tissue-type
or cell line in an organism, where the targeted cells comprise endogenous
thymidine kinase and exogenous DNA, linked to a tissue-specific promoter,
encoding an enzyme that converts a latent toxin to a cell toxin. The only
manipulative step recited in claim 44 is that of “administering to said organism an
amount of said latent toxin effective to trigger generation of said cell toxin by
enzymatic conversion of the latent toxin; thereby inhibiting growth or causing
death of at least a substantial portion of said tissue-type or cell line.”
The examiner rejected the claims as nonenabled, on the basis that the
specification “does not reasonably provide enablement for a method of
selectively inhibiting the growth or causing death of all tissue types in any and all
intact organisms comprising producing all transgenic organisms comprising DNA
encoding and expressing any and all exogenous enzymes that selectively
convert a latent toxin into a cell toxin, wherein said DNA is operatively linked to a
promoter specific for any and all tissue types.” Examiner’s Answer, page 4.2 The
examiner thus concluded that the claims were overly broad with respect to the

1 We will, however, consider claims 40 and 41 separately, for reasons that are explained infra.
2 The examiner also concluded that the specification does not “enable methods of selectively
inhibiting the growth or causing death of all tissue types in any and all intact organisms
comprising using any and all methods of gene therapy.” Id. For reasons that will become clear,
we need address this basis of the rejection only with regard to claims 40 and 41.
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scope of: (1) the tissue types subject to ablation; (2) the organisms in which the
method is carried out; (3) the exogenous enzymes expressed; and (4) the tissue-
specific promoter used.
With respect to the scope of tissue types, organisms, and promoters, the
examiner has not convincingly shown that undue experimentation would have
been required to practice the claimed method. The specification provides a list of
tissue-specific promoters that are expressed only in B-lymphocytes, specific
populations of T-lymphocytes, pituitary cells, and adrenal medullary and
sympathetic neuron cells. See page 8. The specification also states that the
exogenous DNA can be introduced into the appropriate cells by a variety of
known methods, including infection with retroviral constructs, microinjection, or
transfection. See pages 11-12. Finally, the specification provides working
examples showing specific killing, upon exposure to a nucleoside analog, of
spleen and thymus cells (and lymphoma cells in one experiment) in transgenic
mice transformed with a construct encoding HSV-TK under the control of an
immunoglobulin light-chain promoter and heavy-chain gene enhancer. See
pages 23-37.
The examiner has conceded that the specification is enabling for ablation
of lymphoid cells in mice using the exemplified system (Examiner’s Answer, page
6), but asserted that the record lacks evidence to show that “transgenic animals
of any and all species [could be produced] such that specific ablation of a desired
cell population can be achieved without undue experimentation.” Examiner’s
Answer, page 6. The examiner concluded that the enabling scope of the
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specification was limited to the single embodiment specifically exemplified.
Examiner’s Answer, page 8.
The examiner has not shown, however, that undue experimentation would
have been required to practice the claimed method in species other than mice, or
to substitute other tissue-specific promoters for the exemplified lymphoid-specific
promoter in order to ablate cells of other tissues. The examiner carries the initial
burden of showing nonenablement. In re Wright, 999 F.2d 1557, 1561-62, 27
USPQ2d 1510, 1513 (Fed. Cir. 1993). (“When rejecting a claim under the
enablement requirement of section 112, the PTO bears an initial burden of
setting forth a reasonable explanation as to why it believes that the scope of
protection provided by that claim is not adequately enabled by the description of
the invention provided in the specification of the application.”).
In this case, the examiner relies heavily on “the unpredictability of the
transgenic art.” See the Examiner’s Answer, page 6 (emphasis in original): “It
was well known in the art that the expression of a transgene and the effects of its
expression on the animal as a whole are not predictable due to numerous
uncontrollable factors such as the site of integration and methylation-inactivation
of the transgene. See Kappel et al., the right column of page 549.” We can
accept for the sake of argument that the transgenic art in general is subject to a
large amount of unpredictability. Here, however, Appellants have demonstrated
that this unpredictability does not prevent the claimed method from specifically
ablating lymphoid cells in mice. Thus, the evidence shows that the sources of
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unpredictability cited by the examiner did not prevent the method from having its
intended effect in vivo.
The examiner, in considering enablement, appears not to have given
appropriate weight to Appellants’ demonstrated success. That is, since the
claimed method has been demonstrated in mice, with a HSV-TK expression
construct under the control of a lymphoid-specific promoter, the question with
respect to enablement is: would undue experimentation have been required to
extrapolate from that successful experiment to practice the claimed method in
other organisms, with other tissue-specific promoters, or with other toxin-
converting enzymes? The examiner has not presented adequate evidence or
reasoning to show that it would have required undue experimentation to
extrapolate the exemplified method to other organisms, to identify and obtain
other tissue-specific promoters, or to substitute other tissue-specific promoters
with a reasonable expectation of causing a similar effect in other tissues. Thus,
we conclude that these factors cannot support a rejection for nonenablement.
However, we agree with the examiner that the specification does not
provide adequate guidance to enable practice of the claimed method using any
“DNA encoding and expressing an exogenous enzyme that selectively converts a
latent toxin into a cell toxin” in the targeted cells. The only gene identified in the
specification as encoding an enzyme meeting this limitation is the HSV-TK gene.
See, e.g., page 15. The working examples disclosed in the specification all use
the HSV-TK/nucleoside analog system. The specification provides no
meaningful guidance with respect to other genes that meet the criteria recited in
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the claims or the latent toxin(s) that the encoded enzyme would act on to convert
into a cell toxin.
The only guidance provided in the specification with regard to other
enzymes is that “[o]ther enzymes which can be used in the practice of the
present invention are non-mammalian, i.e., enzymes which are not native to the
host cells contemplated for the generation of a transgenic cell population.” Page
15. Essentially, this passage simply states that other exogenous enzymes that
can be used are exogenous enzymes. This “guidance” does nothing to reduce
the experimentation that the skilled artisan would have to undertake in order to
practice the invention as broadly as it is claimed.
“Whether undue experimentation is needed is not a single, simple factual
determination, but rather is a conclusion reached by weighing many factual
considerations.” In re Wands, 858 F.2d 731, 737, 8 USPQ2d 1400, 1404 (Fed.
Cir. 1988). Those considerations include “(1) the quantity of experimentation
necessary, (2) the amount of direction or guidance presented, (3) the presence
or absence of working examples, (4) the nature of the invention, (5) the state of
the prior art, (6) the relative skill of those in the art, (7) the predictability or
unpredictability of the art, and (8) the breadth of the claims.” Id.
Here, most of the Wands factors tend to show that the claims are not fully
enabled. Claim 44 reads on a method of using any enzyme that converts any
nontoxic compound into a toxic compound. Thus, the claims are very broad;
much broader than the guidance and working examples provided in the
specification, which are limited to HSV-TK.
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The state of the prior art does not appear to contribute significantly to the
enabling scope of the disclosure. Mullen discusses “metabolic suicide genes”
which appear to meet the criteria recited in the claims. However, Mullen was
published in 1994, while the instant application claims an effective filing date at
least as early as 1990. Thus, Mullen’s disclosure does not appear to reflect the
state of the art as of the relevant date. See Hybritech, Inc. v. Monoclonal
Antibodies, Inc., 802 F.2d 1367, 1384, 231 USPQ 81, 94 (Fed. Cir. 1987)
(“Enablement . . . is determined as of the filing date of the patent application.”).
In addition, Mullen identifies only three metabolic suicide gene systems,
one of which is the HSV-TK system. The other systems discussed by Mullen are
the cytosine deaminase system and the varicella thymidine kinase system. With
one exception, the references cited by Mullen with respect to these other enzyme
systems were all published after 1990. The only exception concerns a “non-
genetic” approach of coupling cytosine deaminase enzyme to a tumor-specific
antibody; an approach very different from the claimed method. Thus, the prior art
of record does not reflect that other DNAs encoding enzymes meeting the
limitations of the instant claims were known in the art as of the application’s
effective filing date.
The examiner has provided evidence that expression of transgenes was
unpredictable. See the Examiner’s Answer, pages 5 and 6. This evidence is
relevant here, where no other genes encompassed by the claims have been
exemplified, or even identified. The examiner’s evidence shows that the
disclosed success with HSV-TK in mice would not have been viewed by those in
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the art as predictive of other enzymes being expressed at an adequate level to
cause cell ablation in the presence of the appropriate nontoxic precursor
compound.
Finally, the specification shows that a substantial amount of
experimentation is required to carry out the experiments required to make new
constructs comprising other genes and to test such constructs in vitro and in vivo
to determine whether tissue-specific expression of the transgene can be
achieved and whether such expression results in tissue-specific cell ablation in
intact organisms. See pages 20-37 (working examples showing tissue-specific
ablation using the HSV-TK system).
We can assume, based on the technical sophistication of the references,
that the level of skill in the art was high. However, as we have found supra, the
balance of the Wands factors indicates that the claims are not commensurate in
scope with the disclosure. Therefore, we agree with the examiner that claim 44
does not meet the enablement requirement of 35 U.S.C. § 112, first paragraph.
Appellants argue that
the sole act required in the practice of the invention, as defined by
claim 44 is “administering to said organism an amount of said latent
toxin effective to trigger generation of said cell toxin by enzymatic
conversion of the latent toxin”. This act implicitly requires that the
practitioner choose a latent toxin that is “effective” to promote the
required result of being converted by the enzyme expressed in the
target tissue, but it does not require the practitioner to create a
transgenic animal.

That the organism to be treated already contains a tissue-type or
cell line that comprises endogenous thymidine kinase and DNA
encoding and expressing an exogenous enzyme under the control
of a tissue specific promoter is a precondition analogous to that in
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most “method of treatment” claims wherein the subject to be treated
is said to be “in need of” the drug administered. In such a claim,
creation of the precondition is not required of the one who would
practice the treatment claim. It is respectfully submitted that the
burden of creating a transgenic animal should be relegated to those
who submit claims reciting acts that lead to the production of
transgenic animals.

Appeal Brief, page 9 (emphasis in original).
This argument is not persuasive. Appellants argue, in a nutshell, that the
only manipulative step actually recited in the claim is administering a latent toxin
to a transgenic organism, and therefore that is all that must be enabled by the
specification. However, it is indisputable that practicing the claimed method
requires that the transgenic animal recited in the claims be available for
treatment. Appellants have presented no evidence to show that a “stable” of
appropriate transgenic animals are available in the art, such that they can be
obtained by the skilled artisan without experimentation. Thus, it would appear
from the record that the only way for a person of skill in the art to obtain a
transgenic animal expressing an exogenous converting enzyme, such as that
recited in claim 44, would be to make it following the guidance provided in the
specification. That the claim does not expressly recite the manipulative steps
required to do so is of no importance; those steps are required to practice the
claimed method, even if they are not expressly recited in the claims. In order to
enabled the claimed method, therefore, the specification must enable those
skilled in the art to make the recited transgenic organisms.
Appellants also argue that the specification is enabling “[e]ven if the claims
were to be read as requiring creation of an organism containing a transgene.”
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Appeal Brief, page 12. Appellants cite to a declaration submitted under 37 CFR
§ 1.132 as showing evidence that “the specification fully enables insertion of a
transgene into an animal.” Id. Appellants also cite Palmiter3 as showing that
“methods for creating a transgenic animal expressing an exogenous protein
under the control of a tissue specific promoter were known to those of skill in the
art.” Id. Finally, Appellants argue that “the Specification contains detailed
information about types of tissue specific promoters, the cell types for which they
are specific, enhancers for such promoters and the like that can be utilized in the
practice of the invention methods.” Id., page 13.
This argument is also not persuasive. None of the evidence cited by
Appellants – the Evans declaration, Palmiter, and the cited passages from the
specification – is directed to the aspect of the examiner’s rejection on which we
rely. Specifically, none of these sources provides evidence that, based on the
specification and what was known in the art, a skilled artisan would have been
able to practice the claimed invention with converting enzymes other than HSV-
TK without undue experimentation. Therefore, none of the cited evidence
overcomes the rejection for nonenablement.
Although Appellants elected to let the claims stand or fall together, we
think it is appropriate to treat claims 40 and 41 separately. Claims 40 and 41 are
directed to the method of claim 44, where the exogenous gene is HSV-TK. Thus,
claims 40 and 41 do not share the infirmity on which we have based our

3 Palmiter et al., “Cell lineage ablation in transgenic mice by cell-specific expression of a toxin
gene,” Cell, Vol. 50, pp. 435-443 (1987).
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conclusion of nonenablement. As we discussed above, the remaining grounds
set out by the examiner are inadequate to support the rejection. Therefore, the
examiner has not shown that claims 40 and 41 are not enabled for a method of
making transgenic organisms.
In addition to the “transgenic animals” analysis discussed in detail above,
the examiner set out a second enablement analysis, based on the disclosed use
of the claimed system in gene therapy. We do not agree that any potential
problems that might be encountered using the claimed system in gene therapy
support a rejection for nonenablement. The specification discloses that the
claimed method can be used to “create valuable animal models.” Page 19.
There is no rejection for lack of utility before us, and the examiner has conceded
that the claims are enabled with respect to mice lacking lymphoid cells. See the
Examiner’s Answer, page 4. Thus, the examiner does not appear to dispute that
tissue-specific cell ablation would be useful in making animal models for
research.
“The enablement requirement is met if the description enables any mode
of making and using the invention.” Johns Hopkins Univ. v. CellPro Inc., 152
F.3d 1342, 1361, 47 USPQ2d 1705, 1714 (Fed. Cir. 1998) (quoting Engel Indus.,
Inc. v. Lockformer Co., 946 F.2d 1528, 1533, 20 USPQ2d 1300, 1304 (Fed. Cir.
1991)). Since the specification describes one method of making and using the
invention of claims 40 and 41, it enables these claims, whether or not the claimed
method is also enabled for use in gene therapy. Therefore, we reverse the
examiner’s rejection with respect to claims 40 and 41.
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Summary
We affirm the rejection of claims 3-8, 12, 29, 31-39, 44, and 45, because
the examiner has provided evidence to show that practicing the full scope of
these claims would have required undue experimentation, and Appellants have
not effectively rebutted the rejection. However, we reverse the rejection of claims
40 and 41 because they are limited to use of the HSV-TK gene in the claimed
method.
No time period for taking any subsequent action in connection with this
appeal may be extended under 37 CFR § 1.136(a).
AFFIRMED IN PART

TONI R. SCHEINER )
Administrative Patent Judge )
)
)
) BOARD OF PATENT
DONALD E. ADAMS )
Administrative Patent Judge ) APPEALS AND
)
) INTERFERENCES
)
ERIC GRIMES )
Administrative Patent Judge )

Appeal No. 2001-1293 Page 15
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STEPHEN E. REITER
GRAY CARY WARE & FREIDENRICH
4365 EXECUTIVE DRIVE, SUITE 1600
SAN DIEGO, CA 92121

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